Compared with the traditional weather radar, the hardware of the dual polarization weather radar has changed greatly, especially in the receiver and antenna feeder. The change of hardware makes the diagnosis method of dual polarization radar different. This paper analyzes the difference between Sband dual polarization weather radar and single polarization radar in fault diagnosis by comparing with traditional weather radar in hardware structure and calibration channel. This article proposes two diagnostic techniques: isolating the main channel and test channel by the dual signal source and dynamic method; segmenting the main channel by the dual signal source and sun calibration. The article gives the fault cases of dual polarization radar, which can provide a reference for the planned upgrading of the dual polarization radar, and also provide a reference for the troubleshooting of the dual polarization radar at the radar stations.