diff --git a/inputmethod/BUILD.gn b/inputmethod/BUILD.gn
index cc1480cdb87beca13fa1874a4530dd6e8ab67a50..ef0543708dd53bc92f05fcad29c17be96c7b8790 100644
--- a/inputmethod/BUILD.gn
+++ b/inputmethod/BUILD.gn
@@ -24,6 +24,7 @@ ohos_ndk_library("libohinputmethod") {
     "./inputmethod/inputmethod_attach_options_capi.h",
     "./inputmethod/inputmethod_cursor_info_capi.h",
     "./inputmethod/inputmethod_inputmethod_proxy_capi.h",
+    "./inputmethod/inputmethod_message_handler_proxy_capi.h",
     "./inputmethod/inputmethod_private_command_capi.h",
     "./inputmethod/inputmethod_text_avoid_info_capi.h",
     "./inputmethod/inputmethod_text_config_capi.h",
@@ -39,6 +40,7 @@ ohos_ndk_headers("libohinputmethod_header") {
     "./include/inputmethod_controller_capi.h",
     "./include/inputmethod_cursor_info_capi.h",
     "./include/inputmethod_inputmethod_proxy_capi.h",
+    "./include/inputmethod_message_handler_proxy_capi.h",
     "./include/inputmethod_private_command_capi.h",
     "./include/inputmethod_text_avoid_info_capi.h",
     "./include/inputmethod_text_config_capi.h",
diff --git a/inputmethod/include/inputmethod_inputmethod_proxy_capi.h b/inputmethod/include/inputmethod_inputmethod_proxy_capi.h
index f8257c2b6307f7237a2f11f46b4fbf05e44057b9..3d6dd29b1618ac41371651b20268df64d57a7c3a 100644
--- a/inputmethod/include/inputmethod_inputmethod_proxy_capi.h
+++ b/inputmethod/include/inputmethod_inputmethod_proxy_capi.h
@@ -39,6 +39,7 @@
 #include "inputmethod_types_capi.h"
 #include "inputmethod_cursor_info_capi.h"
 #include "inputmethod_private_command_capi.h"
+#include "inputmethod_message_handler_proxy_capi.h"
 #ifdef __cplusplus
 extern "C"{
 #endif /* __cplusplus */
@@ -166,6 +167,48 @@ InputMethod_ErrorCode OH_InputMethodProxy_NotifyCursorUpdate(
  */
 InputMethod_ErrorCode OH_InputMethodProxy_SendPrivateCommand(
     InputMethod_InputMethodProxy *inputMethodProxy, InputMethod_PrivateCommand *privateCommand[], size_t size);
+
+/**
+ * @brief Send customize message.
+ *
+ * @param inputMethodProxy Represents a pointer to an {@link OH_InputMethod_InputMethodProxy} instance.
+ *     The inputMethodProxy is obtained from {@link OH_InputMethodController_Attach}.
+ * @param msgId The message id. Max size 256B.
+ * @param msgIdLength The size of message id. Max is 256B.
+ * @param msgParam The message param. Max size 128KB.
+ * @param msgParamLength The size of message param. Max is 128KB.
+ * @return Returns a specific error code.
+ *     {@link IME_ERR_OK} - success.
+ *     {@link IME_ERR_PARAMCHECK} - parameter check failed.
+ *     {@link IME_ERR_IMCLIENT} - input method client error.
+ *     {@link IME_ERR_DETACHED} - input method client detached.
+ *     {@link IME_ERR_NULL_POINTER} - unexpected null pointer.
+ *     {@link IME_ERR_REQUEST_NOT_ACCEPT} - another side was not register.
+ *     {@link IME_ERR_BASIC_MODE} - ime security mode is basic mode.
+ *     {@link IME_ERR_EDITABLE} - current is not editable status.
+ * Specific error codes can be referenced {@link InputMethod_ErrorCode}.
+ * @since 16
+ */
+InputMethod_ErrorCode OH_InputMethodProxy_SendMessage(InputMethod_InputMethodProxy *inputMethodProxy,
+    const char16_t *msgId, size_t msgIdLength, const uint8_t *msgParam, size_t msgParamLength);
+
+/**
+ * @brief Register message handler.
+ *
+ * @param inputMethodProxy Represents a pointer to an {@link OH_InputMethod_InputMethodProxy} instance.
+ *     The inputMethodProxy is obtained from {@link OH_InputMethodController_Attach}.
+ * @param messageHandler Represents a pointer to an {@link InputMethod_MessageHandlerProxy} instance.
+ *     The caller needs to manage the lifecycle of messageHandler.
+ * @return Returns a specific error code.
+ *     {@link IME_ERR_OK} - success.
+ *     {@link IME_ERR_PARAMCHECK} - parameter check failed.
+ *     {@link IME_ERR_DETACHED} - input method client detached.
+ *     {@link IME_ERR_NULL_POINTER} - unexpected null pointer.
+ * Specific error codes can be referenced {@link InputMethod_ErrorCode}.
+ * @since 16
+ */
+InputMethod_ErrorCode OH_InputMethodProxy_RecvMessage(
+    InputMethod_InputMethodProxy *inputMethodProxy, InputMethod_MessageHandlerProxy *messageHandler);
 #ifdef __cplusplus
 }
 #endif /* __cplusplus */
diff --git a/inputmethod/include/inputmethod_message_handler_proxy_capi.h b/inputmethod/include/inputmethod_message_handler_proxy_capi.h
new file mode 100644
index 0000000000000000000000000000000000000000..65c60e46dbb3ed53670325dbd37f15105893f007
--- /dev/null
+++ b/inputmethod/include/inputmethod_message_handler_proxy_capi.h
@@ -0,0 +1,170 @@
+/*
+ * Copyright (c) 2024 Huawei Device Co., Ltd.
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+#ifndef OHOS_INPUTMETHOD_MESSAGE_HANDLER_PROXY_CAPI_H
+#define OHOS_INPUTMETHOD_MESSAGE_HANDLER_PROXY_CAPI_H
+/**
+ * @addtogroup InputMethod
+ * @{
+ *
+ * @brief InputMethod provides functions to use input methods and develop input methods.
+ *
+ * @since 16
+ */
+
+/**
+ * @file inputmethod_message_handler_proxy_capi.h
+ *
+ * @brief Provides functions for sending and receiving customize message from input method.
+ *
+ * @library libohinputmethod.so
+ * @kit IMEKit
+ * @syscap SystemCapability.MiscServices.InputMethodFramework
+ * @since 16
+ * @version 1.0
+ */
+#include <stddef.h>
+
+#include "inputmethod_text_config_capi.h"
+#include "inputmethod_types_capi.h"
+#ifdef __cplusplus
+extern "C" {
+#endif /* __cplusplus */
+/**
+ * @brief Define the InputMethod_MessageHandlerProxy structure type.
+ *
+ * Provides methods for sending and receiving customize message.\n
+ * When input method sends customize message or unregister message handler, the methods will be called.\n
+ *
+ * @since 16
+ */
+typedef struct InputMethod_MessageHandlerProxy InputMethod_MessageHandlerProxy;
+
+/**
+ * @brief Called when unregister messager handler.
+ *
+ * You need to implement this function, set it to {@link InputMethod_MessageHandlerProxy} through {@link
+ * OH_MessageHandlerProxy_SetOnTerminatedFunc}, and use {@link OH_InputMethodProxy_RecvMessage} to complete the
+ * registration.\n
+ *
+ * @param messageHandlerProxy Represents a pointer to an
+ *                            {@link InputMethod_MessageHandlerProxy} instance which will be set in.
+ * @return Returns the result of handling private command.
+ * @since 16
+ */
+typedef int32_t (*OH_MessageHandlerProxy_OnTerminatedFunc)(InputMethod_MessageHandlerProxy *messageHandlerProxy);
+
+/**
+ * @brief Called when receiving customize message from input method.
+ *
+ * You need to implement this function, set it to {@link InputMethod_MessageHandlerProxy} through {@link
+ * OH_MessageHandlerProxy_SetOnTerminatedFunc}, and use {@link OH_InputMethodProxy_RecvMessage} to complete the
+ * registration.\n
+ *
+ * @param messageHandlerProxy Represents a pointer to an
+ *                            {@link InputMethod_MessageHandlerProxy} instance which will be set in.
+ * @param msgId ArrayBuffer.msgId from input method.
+ * @param msgIdLength Size of ArrayBuffer.msgId.
+ * @param msgParam ArrayBuffer.msgParam from input method.
+ * @param msgParamLength Size of ArrayBuffer.msgParam.
+ * @since 16
+ */
+typedef int32_t (*OH_MessageHandlerProxy_OnMessageFunc)(InputMethod_MessageHandlerProxy *messageHandlerProxy,
+    const char16_t msgId[], size_t msgIdLength, const uint8_t *msgParam, size_t msgParamLength);
+
+/**
+ * @brief Create a new {@link InputMethod_MessageHandlerProxy} instance.
+ *
+ * @return If the creation succeeds, a pointer to the newly created {@link InputMethod_MessageHandlerProxy}
+ * instance is returned. If the creation fails, NULL is returned, possible cause is insufficient memory.
+ * @since 16
+ */
+InputMethod_MessageHandlerProxy *OH_MessageHandlerProxy_Create(void);
+
+/**
+ * @brief Destroy a {@link InputMethod_MessageHandlerProxy} instance.
+ *
+ * @param proxy The {@link InputMethod_MessageHandlerProxy} instance to be destroyed.
+ * @since 16
+ */
+void OH_MessageHandlerProxy_Destroy(InputMethod_MessageHandlerProxy *proxy);
+
+/**
+ * @brief Set function {@link OH_MessageHandlerProxy_OnTerminatedFunc} into {@link InputMethod_MessageHandlerProxy}.
+ *
+ * @param proxy Represents a pointer to an
+ *              {@link InputMethod_MessageHandlerProxy} instance which will be set function in.
+ * @param onTerminatedFunc Represents function {@link OH_MessageHandlerProxy_SetOnTerminatedFunc} which
+ * will be set.
+ * @return Returns a specific error code.
+ *     {@link IME_ERR_OK} - success.
+ *     {@link IME_ERR_NULL_POINTER} - unexpected null pointer.
+ * Specific error codes can be referenced {@link InputMethod_ErrorCode}.
+ * @since 16
+ */
+InputMethod_ErrorCode OH_MessageHandlerProxy_SetOnTerminatedFunc(
+    InputMethod_MessageHandlerProxy *proxy, OH_MessageHandlerProxy_OnTerminatedFunc onTerminatedFunc);
+
+/**
+ * @brief Get function {@link OH_MessageHandlerProxy_OnTerminatedFunc} from {@link InputMethod_MessageHandlerProxy}.
+ *
+ * @param proxy Represents a pointer to an
+ *              {@link InputMethod_MessageHandlerProxy} instance which will be get function from.
+ * @param onTerminatedFunc Represents function {@link OH_MessageHandlerProxy_GetOnTerminatedFunc} which
+ * will be get.
+ * @return Returns a specific error code.
+ *     {@link IME_ERR_OK} - success.
+ *     {@link IME_ERR_NULL_POINTER} - unexpected null pointer.
+ * Specific error codes can be referenced {@link InputMethod_ErrorCode}.
+ * @since 16
+ */
+InputMethod_ErrorCode OH_MessageHandlerProxy_GetOnTerminatedFunc(
+    InputMethod_MessageHandlerProxy *proxy, OH_MessageHandlerProxy_OnTerminatedFunc *onTerminatedFunc);
+
+/**
+ * @brief Set function {@link OH_MessageHandlerProxy_OnMessageFunc} into {@link InputMethod_MessageHandlerProxy}.
+ *
+ * @param proxy Represents a pointer to an
+ *              {@link InputMethod_MessageHandlerProxy} instance which will be set function in.
+ * @param onMessageFunc Represents function {@link OH_MessageHandlerProxy_SetOnMessageFunc} which
+ * will be set.
+ * @return Returns a specific error code.
+ *     {@link IME_ERR_OK} - success.
+ *     {@link IME_ERR_NULL_POINTER} - unexpected null pointer.
+ * Specific error codes can be referenced {@link InputMethod_ErrorCode}.
+ * @since 16
+ */
+InputMethod_ErrorCode OH_MessageHandlerProxy_SetOnMessageFunc(
+    InputMethod_MessageHandlerProxy *proxy, OH_MessageHandlerProxy_OnMessageFunc onMessageFunc);
+
+/**
+ * @brief Get function {@link OH_MessageHandlerProxy_OnMessageFunc} from {@link InputMethod_MessageHandlerProxy}.
+ *
+ * @param proxy Represents a pointer to an {@link InputMethod_MessageHandlerProxy} instance which will be get function
+ * from.
+ * @param onMessageFunc Represents function {@link OH_MessageHandlerProxy_GetOnMessageFunc} which
+ * will be get.
+ * @return Returns a specific error code.
+ *     {@link IME_ERR_OK} - success.
+ *     {@link IME_ERR_NULL_POINTER} - unexpected null pointer.
+ * Specific error codes can be referenced {@link InputMethod_ErrorCode}.
+ * @since 16
+ */
+InputMethod_ErrorCode OH_MessageHandlerProxy_GetOnMessageFunc(
+    InputMethod_MessageHandlerProxy *proxy, OH_MessageHandlerProxy_OnMessageFunc *onMessageFunc);
+#ifdef __cplusplus
+}
+#endif /* __cplusplus */
+/** @} */
+#endif // OHOS_INPUTMETHOD_MESSAGE_HANDLER_PROXY_CAPI_H
\ No newline at end of file
diff --git a/inputmethod/include/inputmethod_types_capi.h b/inputmethod/include/inputmethod_types_capi.h
index 0fc88c45514054cb20d41bcc77506692d228bc60..1c1ba5c1b831577514ea45f3185bd0b4b06c3c3d 100644
--- a/inputmethod/include/inputmethod_types_capi.h
+++ b/inputmethod/include/inputmethod_types_capi.h
@@ -251,7 +251,6 @@ typedef enum InputMethod_ErrorCode {
      * @error The error code in the correct case.
      */
     IME_ERR_OK = 0,
-
     /**
      * @error The error code when error is undefined.
      */
@@ -292,6 +291,21 @@ typedef enum InputMethod_ErrorCode {
      * @error The error code when input method client detached.
      */
     IME_ERR_DETACHED = 12800009,
+    /**
+     * @error The error code when current security mode is basic mode.
+     * @since 16
+     */
+    IME_ERR_BASIC_MODE = 12800014,
+    /**
+     * @error The error code when another size was not register message handler.
+     * @since 16
+     */
+    IME_ERR_REQUEST_NOT_ACCEPT = 12800015,
+    /**
+     * @error The error code when current is not editable status.
+     * @since 16
+     */
+    IME_ERR_EDITABLE = 12800016,
     /**
      * @error The error code when unexpected null pointer.
      */