The invention discloses a method for negotiating a voice encoding/decoding format in a communication system, in which a caller mobile station originates to negotiate the voice encoding/decoding formatwith a callee mobile station, the method comprises that: a mobile switch centre of the communication system receives an originating signal transmitted by the caller mobile station, the originating signal carries the number of the callee mobile station; a voice encoding/decoding format list which is latest used by the callee mobile station is acquired according to the originating signal in a database in which mobile station information is stored; the voice encoding/decoding format used when the caller mobile station is communicated with the callee mobile station is determined, and voice carrier of the caller mobile station and the callee mobile station is established in the voice encoding/decoding format. The invention omits a carrier update step, enhances a continuation speed. The invention also discloses a system for negotiating a voice encoding/decoding format in a communication system.