The present invention discloses a method and a system for implementing communications between multiple subnets covered by one physical Mobile Switching Center (MSC) and an MSC. The method includes the steps of: mapping one physical MSC to multiple logical MSCs, i.e. multiple virtual MSCs, and assigning a virtual MSC number to each virtual MSC, and setting relationship(s) between location area(s) covered by the virtual MSC and the virtual MSC number of each virtual MSC; transmitting location information of a terminal with the virtual MSC number during communications to implement communications among multiple subnets. During communication, since the terminal location is transmitted according to the virtual MSC number, it is possible to differentiate the terminals located in different subnets covered by a physical MSC, therefore the roaming and handover of the terminal between the subnets can be implemented; and the roaming limitation also can be implemented through the MSC List and VLR List.