Insufficient welding or bad welding of motor armature is one of the main faults of motor armature. With the help of the application of multi-agent technology in the fault diagnosis system of motor armature to detect insufficient welding or bad welding, the intelligent description of the various faults has been enhanced, also, the capacity of fault diagnosis of the system have been greatly optimized and improved. In this paper, we first analyses the characteristics of the fault of motor armature with insufficient welding or bad welding, by which the characteristics of the fault are identified. Next, we introduces agent and multi-agent system. Finally, the building of fault diagnosis system based on multi-agent technology is discussed.