A method for processing deferred messages includes a storing process, a notification process and a retrieving process. In the storing process, when a user presets and requires to store the deferred message, the system stores the deferred message to be sent to the user; in the notification process, when a user gets online, an IM server at the client side detects the system has stored the deferred message for the user and if the user has subscribed the deferred message notification, the system sends the deferred message notification to the client according to the setting of the system or of the user; in the retrieving process, when the client receives the deferred message notification and requests to acquire the deferred message, its IM server sends the deferred message content to the client. The present invention improves the method for processing deferred messages in the SIP/SIMPLE IM service system.