PoC is a half-duplex PTT service using VoIP technology based on cellular network packet domain carrying. However PoC uses the standard Session Initiation Protocol (SIP) to setup session. The standard SIP signaling is too long, which brings more setup delay and does not hold true the wireless communication network, so it must be cut. This paper researchs the method to reduce PoC session setup delay from SIP session cut. We achieve the testing results in the actual commercial network. The results shows that this method can effectivly shorten the PoC session setup delay.