This invention discloses a method and system of implementing a ring back tone based on a group mobile switchboard service. The method includes: a home service control point of the group mobile switchboard obtaining an identification of an extension subscriber which a calling party calls, and sending routing information of a ring back tone intelligent peripheral and the identification of the called extension subscriber respectively to a gateway mobile switching center/mobile switching center which triggers the intelligent service; the gateway mobile switching center/mobile switching center which triggers the intelligent service routing the identification of the called extension subscriber to the ring back tone intelligent peripheral according to the received routing information of the ring back tone intelligent peripheral; the ring back tone intelligent peripheral connecting the call to a visited mobile switching center of the called extension subscriber, and playing a group ring back tone subscribed to by the group customer for the calling party. This invention can play a group ring back tone subscribed to by the group customer for a subscriber during the transfer from a switchboard to an extension.