Abstract: Cu-Al transition lug can reduce the weight and cost of the components and give full play to the performance advantages of their materials. It is an important connecting component in the active power system and is widely used in the power system. The reasons leading to fracture for Cu-Al transition lug of electric pump after 6 years operation was analyzed by means of morphology analysis, hardness test, metallographic test, SEM and other detection means. The results show that the welding process control of the Cu-Al transition lug is poor, which is resulting in incomplete plastic deformation, copper slag inclusion, holes and other defects. The cracks were formed and further expansion during the service, which the cause of the electrochemical corrosion at the above defects.