In order to adapt to the requirements and higher performance of train passenger information system (PIS), the design scheme of SIPbased PIS was proposed, in which a detailed solution for the train intercom and broadcast based on SIP was introduced. The session management and media negotiation were completed by fully using the SIP methods and SDP negotiation mechanisms. To verify the feasibility of the audio control unit, a software architecture and various software modules were implemented. The experimental result shows that the train audio control unit can accurately complete all the preset functions.