Abstract: A new method for automatically diagnosing broken-bar fault of rotor of asynchronous motor was proposed in the paper,which taking extended Park’s vector approach to pick up the fault(characte)-(ristics) and using BP network to recognize the mode of fault.When the method was applied, hiding effect of foundational frequency in fault characteristic was removed,and artificial interference was avoided.The(results) of practical example indicated that the method has good effectiveness and accuracy.