In order to reduce the traffic accidents in expressway, a system which can monitor vehicles in expressway has been designed. The system uses GPS to collect vehicle information, and then the data be transmitted to sever through the GPRS, a judgement can be made on the vehicle itself and its surrounding running condition with a specific pre-warning algorithm and driver can receive the automatic warning if there are illegal driving behaviors. The improved schemes on memory scheduling of sever and disconnection of vehicle terminals are be respectively proposed. Finally, the stability of system, the processing efficiency of pre-warning events and accuracy of pre-warning are tested in the simulation environment with LAN, the results show that the system has higher stability and accuracy; it can be referred in further studies on the research of monitoring expressway.