Abstract: Long term effect of defective points in main electrical circuit of catenary could increase device temperature, lose mechanical strength, cause the carrier cable broken, break the joint points. This article used infrared imaging technology to implement the state detection system of main electrical circuit of on-board carenary, complete the online automation detection of the main electrical circuit of the catenary. The system was tested and operated on the highspeed integrated inspection train. The function of the system was verified. The system could be used to guide the maintenance and repair of catenary equipment.