JC-311 passive wireless temperature online monitoring system uses surface acoustic wave (SAW) devices as sensors, combined with wireless temperature collectors to realize the collection and transmission of sensor information. The sensors are installed on the measured point and can be connected without a connection. The temperature information of the measured point is transmitted. The sensor itself does not need power supply, and does not need to take electricity from the power equipment, so it has outstanding safety, reliability and maintainability. This technology is a disruptive technology in the safety online monitoring of high-voltage equipment, and is a breakthrough in the real-time temperature monitoring technology of high-voltage equipment in smart grids.