In recent years, the microwave power sensor taking planar potential barrier diode as core component that coordinates with small power meter makes the high speed, high precision and successive power measurements and thus comes into realization. It is widely used to measure high frequency equipment such as the weather radar signal power. The paper analyzes the characteristics and circuit principle of microwave power sensor, introduces the connecting and setting methods with power meter and discusses the method to judge the fault of new generation weather radar by using microwave power sensor in the two typical maintenances of CINRAD/SA as examples.