The invention discloses a soft-switching residential area assigning method and a BSC (base station controller) for a trunking communication system. In the method, the BSC receives pilot-frequency environmental measurement report domains from one or more terminal UE (user equipment) in a scheduling period, selects residential areas in the preset quantity from the residential areas indicated by all the pilot-frequency environmental measurement report domains received in the scheduling period, and transmits broadcast channel assigning message carrying information about the residential areas in the preset quantity to one or more UE in the scheduling period. The invention can assign the residential areas for soft switching for a plurality of UE in the trunking communication system at the same time.