A method for processing unstructured supplementary service data, USSD, service implemented by an application server, characterized in that the method further comprises: when the application server determines that a mobile terminal on a voice over Long Term Evolution network supports USSD operations over IP multimedia core network subsystem, sending, by the application server, an invite message to the mobile terminal through a call session control function, CSCF, entity, wherein the invite message comprises an identifier of a USSD service; receiving an invite response, wherein the invite response is sent by the mobile terminal through the CSCF entity and carries reply information entered by a subscriber, and the reply information comprises the identifier of the USSD service; generating, according to the reply information, a message that requests to execute the USSD service, wherein the message that requests to execute the USSD service carries the identifier of the USSD service; and sending, to a subscriber data server, the message that requests to execute the USSD service, so that the subscriber data server processes the USSD service according to the identifier of the USSD service carried in the message that requests to execute the USSD service; wherein before the application server determines that the mobile terminal supports USSD operations over IP multimedia core network subsystem, the method further comprises: receiving a USSD service message sent by the subscriber data server, wherein the USSD service message carries identification information of the mobile terminal and the identifier of the USSD service; determining an access network of the mobile terminal according to the identification information of the mobile terminal; and if the access network of the mobile terminal is the voice over Long Term Evolution network, determining whether the mobile terminal supports USSD operations over IP multimedia core network subsystem. when the application server determines that a mobile terminal on a voice over Long Term Evolution network supports USSD operations over IP multimedia core network subsystem, sending, by the application server, an invite message to the mobile terminal through a call session control function, CSCF, entity, wherein the invite message comprises an identifier of a USSD service; receiving an invite response, wherein the invite response is sent by the mobile terminal through the CSCF entity and carries reply information entered by a subscriber, and the reply information comprises the identifier of the USSD service; generating, according to the reply information, a message that requests to execute the USSD service, wherein the message that requests to execute the USSD service carries the identifier of the USSD service; and sending, to a subscriber data server, the message that requests to execute the USSD service, so that the subscriber data server processes the USSD service according to the identifier of the USSD service carried in the message that requests to execute the USSD service; wherein before the application server determines that the mobile terminal supports USSD operations over IP multimedia core network subsystem, the method further comprises: receiving a USSD service message sent by the subscriber data server, wherein the USSD service message carries identification information of the mobile terminal and the identifier of the USSD service; determining an access network of the mobile terminal according to the identification information of the mobile terminal; and if the access network of the mobile terminal is the voice over Long Term Evolution network, determining whether the mobile terminal supports USSD operations over IP multimedia core network subsystem. receiving a USSD service message sent by the subscriber data server, wherein the USSD service message carries identification information of the mobile terminal and the identifier of the USSD service; determining an access network of the mobile terminal according to the identification information of the mobile terminal; and if the access network of the mobile terminal is the voice over Long Term Evolution network, determining whether the mobile terminal supports USSD operations over IP multimedia core network subsystem.