A method for interworking between a first signaling network and a second signaling network is provided. The first signaling network includes a first signaling point and a signaling transfer point, and the second signaling network includes a second signaling point, the first signaling network is connected with the second signaling network via an interworking point. The method includes: receiving by the interworking point a first signaling point TransFer Prohibited message from the first signaling network; detecting all the links between the interworking point and the first signaling network, if there is any interworking link, dropping the TransFer Prohibited message; otherwise, transmitting a Signaling Unavailable message to the second signaling point. This invention also provides an interworking point of signaling networks and a communication system. In this invention, TFP message in narrowband MTP3 protocol and DUNA message the broadband M3UA protocol are combined for informing the route state.