The motor equivalent circuit method provides an effective method to estimate motor efficiency. However, the circuit parameters normally have to be determined through field tests, which are impossible to conduct when systems are in service. Because motor efficiency and power factor data at four load levels under the rated frequency are always published, an iterative method is proposed to identify the circuit parameters using these published data. In this paper, the mathematical relations between the published data and circuit parameters are first formularized, and then the least squares method is utilized to identify the circuit parameters. Finally, the motor performance is simulated with the identified circuit parameters and compared with the published data. The results show that the simulated motor performance matches well with the published data.