Abstract: As an indispensable part of the power system, the operation state of the switchgear directly affects the safety and stability of the whole power system. Partial discharge(PD) is the main cause of the insulation failure of the switchgear. This paper introduces the causes and classification of local discharge, and discusses the characteristics and propagation path of UHF signal in detail. Subsequently, a set of local discharge detection system based on UHF signal is designed, including the overall architecture of the system, the selection and arrangement of UHF sensor, the data acquisition and processing module, and the signal transmission and storage scheme. The effectiveness of the system is verified through experiments to provide strong technical support for the operation and maintenance of the switch cabinet.