A method for speech Codec negotiation in a communication system that includes a wireless access network and a core network, comprising: receiving, by a mobile switching center emulation in the core network, an originating call signal from a calling user through a message sent from a base station to which the calling user pertains, the originating call signal carrying a number of a called mobile station but no speech Codec list (step 1001); obtaining a latest speech Codec list used by the called mobile station from a database storing mobile station information in accordance with the number of the called mobile station (step 1002); obtaining, by the mobile switching center emulation, a speech Codec list supported by the calling user (step 1003); and determining a speech Codec to be used in a communication between the calling user and the called mobile station, in accordance with the speech Codec list supported by the calling user and the latest speech Codec list used by the called mobile station (step 1004), wherein obtaining the speech Codec list supported by the calling user comprises: obtaining, by the mobile switching center emulation, the speech Codec list supported by the calling user through an interaction with the base station to which the calling user pertains, the interaction comprises: requesting, by the mobile switching center emulation, the calling user to send the speech Codec list supported by the calling user through an Assignment Request message sent from the mobile switching center emulation to the base station; receiving, by the mobile switching center emulation, the speech Codec list supported by the calling user returned by the calling user through an Assignment Complete message sent from the base station to the mobile switching center emulation; wherein when the called mobile station performs a voice communication, the speech Codec list used by the called mobile station is stored in the database, and only a latest speech Codec list used by the called mobile station is stored. receiving, by a mobile switching center emulation in the core network, an originating call signal from a calling user through a message sent from a base station to which the calling user pertains, the originating call signal carrying a number of a called mobile station but no speech Codec list (step 1001); obtaining a latest speech Codec list used by the called mobile station from a database storing mobile station information in accordance with the number of the called mobile station (step 1002); obtaining, by the mobile switching center emulation, a speech Codec list supported by the calling user (step 1003); and determining a speech Codec to be used in a communication between the calling user and the called mobile station, in accordance with the speech Codec list supported by the calling user and the latest speech Codec list used by the called mobile station (step 1004), wherein obtaining the speech Codec list supported by the calling user comprises: obtaining, by the mobile switching center emulation, the speech Codec list supported by the calling user through an interaction with the base station to which the calling user pertains, the interaction comprises: requesting, by the mobile switching center emulation, the calling user to send the speech Codec list supported by the calling user through an Assignment Request message sent from the mobile switching center emulation to the base station; receiving, by the mobile switching center emulation, the speech Codec list supported by the calling user returned by the calling user through an Assignment Complete message sent from the base station to the mobile switching center emulation; wherein when the called mobile station performs a voice communication, the speech Codec list used by the called mobile station is stored in the database, and only a latest speech Codec list used by the called mobile station is stored. obtaining, by the mobile switching center emulation, the speech Codec list supported by the calling user through an interaction with the base station to which the calling user pertains, the interaction comprises: requesting, by the mobile switching center emulation, the calling user to send the speech Codec list supported by the calling user through an Assignment Request message sent from the mobile switching center emulation to the base station; receiving, by the mobile switching center emulation, the speech Codec list supported by the calling user returned by the calling user through an Assignment Complete message sent from the base station to the mobile switching center emulation; wherein when the called mobile station performs a voice communication, the speech Codec list used by the called mobile station is stored in the database, and only a latest speech Codec list used by the called mobile station is stored. requesting, by the mobile switching center emulation, the calling user to send the speech Codec list supported by the calling user through an Assignment Request message sent from the mobile switching center emulation to the base station; receiving, by the mobile switching center emulation, the speech Codec list supported by the calling user returned by the calling user through an Assignment Complete message sent from the base station to the mobile switching center emulation; wherein when the called mobile station performs a voice communication, the speech Codec list used by the called mobile station is stored in the database, and only a latest speech Codec list used by the called mobile station is stored.