A method, base station controller and base station subsystem for monitoring quality of service are applied in the local switch process based on a base station transceiver station (BTS). The method comprises that while service data is switched, the base station controller (BSC) establishes a first real-time transport protocol (RTP) link and a first real-time transport control protocol (RTCP) link between itself and the BTS; the BSC judges whether the both communication parties are in the same BTS, and if yes, the BTS directly transfers the service data, otherwise the BSC controls the two BTSs which are corresponding to the both communication parties to establish a second RTP link and a second RTCP link between the two BTSs and controls the service data to be switched from the first RTP link to the second RTP link; the BSC receives control information which is related to the quality of service and generated and transmitted by the BTS and monitors the quality of service according to the control information.