The invention relates to a diagnosis device for an insulation fault of a power distribution system. The diagnosis device comprises a current transformer, a partial discharge sensor, an infrared thermal imaging sensor, an ARM core processing unit and a man-machine interaction unit. Compared with the prior art, the diagnosis device has the advantages of high integration, multi-source research and judgment, comprehensive analysis based on ultrahigh frequency partial discharge, infrared temperature measurement and current break variable, and determination of the fault type, and is more accurate and efficient. Multiple sensors are fused and applied, the equipment cost is saved, and deployment is convenient. Non-contact installation is mainly adopted, live-line installation is achieved, and power failure is not needed. The diagnosis device has a plurality of network access modes, has a data aggregation function, can access a plurality of data sensing information through a plurality of wireless and wired communication modes, and performs data interaction with a superior system. According to a multi-parameter fusion analysis equipment state diagnosis and early warning technology, various monitoring data can be fused, fusion analysis is carried out, fault deduction is carried out by referring to historical data, and an operation and maintenance strategy is guided.