The present invention discloses a method for processing USSD service. In this method, when an application server determines that a mobile terminal on a VoLTE network supports USSD operations over IMS, the application server sends an invite message to the mobile terminal, where the invite message includes an identifier of a USSD service; receives an invite response from the mobile terminal, where the invite response carries reply information entered by a subscriber and the identifier of the USSD service; generates, according to the reply information, a message that requests to execute the USSD service, where the message that requests to execute the USSD service carries the identifier of the USSD service; and sends, to a subscriber data server, the message that requests to execute the USSD service, so that the subscriber data server processes the USSD service.