Abstract: The concept of voltaic involution was established starting from collected stator current of squirrel cage induction motor, and the voltaic involution was used to enlarge and transfer fault characteristic frequency. The fault diagnosis method of motor based on improved instantaneous power method was proposed according to concept of instantaneous power. The characteristic frequency components of rotor bar breaking fault and rotor eccentricity fault were extracted by theoretical analysis, which can effectively overcome the shortcomings that characteristic frequency of rotor bar breaking fault is likely to be flooded by fundamental frequency, and realize distinguishing and diagnosis of rotor bar breaking fault, eccentricity fault and complex fault. The data need to collect was cut by half and influence of voltage fluctuation and sampling error to instantaneous power was avoided compared with the traditional instantaneous power diagnosis method.