For the early broken rotor bars fault of induction motor, the fault characteristic frequency of the stator current was easily submerged by the fundamental frequency, so the broken rotor bars fault of motor could not be detected in time. Multiple coupled circuit equation was used to establish the model of the broken rotor bars fault occurring in induction motor, and the model of the early broken rotor bars fault of induction motor in dq0 coordinate system was derived. Based on the fault model, the variation curves of motor equivalent parameters were obtained by parameter identification and sliding window technology. These curves had obvious fault characteristic signals for the early broken rotor bars fault, and the characteristics of the curves could be used to diagnose the broken rotor bars fault. The different indexes of the rotor faults with different degrees were given. The experiment verified the feasibility of the proposed method.