According to the behaviors of illegal action that the people who enter into highspeed rail line by using metallic equipment to damage the protecting mesh or barbed wire cage, the paper puts forward a highspeed rail line antiintrusion system based on wireless sensor networks. Combined with the technical features of low power and selforganized network of WSN, the paper constructs the system architecture, the design of data acquisition node. And the scheme of nodes placement are proposed as well. Among them, the data acquisition node is integrated with the passive infrared sensor, ultrasonic sensor and magnetic field sensor. The system alarm information is derived from three sensors’ alarm data by “and operation”. The scheme of relaying nodes placement is mainly studied and a simulation case analysis is used whose outcome of node number error is limited to 10% while the distance between relaying nodes is not more than 140 m. The system can be able to effectively monitor the intrusion behavior into highspeed rail line and ensure train operation safety.