With the increasing degree of automotive electronics, automotive electronic control systems continue to increase and a large amount of these complex systems using electronic chips to perform their own function, making them very difficult to repair. For ease of maintenance, automotive electronic control systems are generally designed with self-diagnostic function, which is usually referred to OBD diagnostic feature that can automatically diagnose faults of systems, store the Diagnostic Trouble Code (DTC) in memory and can be read through the communication port. This article mainly focuses on fault diagnostic method for ECU in electric vehicle based on CAN bus, for electric vehicles are developed very fast in order to solve the energy crisis and environmental pollution. This diagnostic system described in the article has designed a host computer and a lower machine. The development of software in host computer is based on LabVIEW virtual instrument technology and NEC micro-processing chip is used to develop the lower machine, achieving the automatic and controlled ECU test.