Method, device and system for triggering packet domain connection during circuit domain call

The invention discloses a method for triggering packet domain connection within the period of circuit domain communication. The method comprises: a first communication apparatus transmits a circuit domain signaling message to a second communication apparatus during circuit domain communication with the second communication apparatus, wherein the circuit domain signaling message comprises trigger indication information for establishing the packet domain connection; and the second communication apparatus is triggered to establish the packet domain connection with the first communication apparatus through a packet network according to the circuit domain signaling message. The invention simultaneously discloses a communication apparatus and a communication system. The invention can strengthenthe reliability of triggering the packet domain connection and shorten the duration of end-to-end packet domain connection establishment.