In order to study the response mechanism for motor stator current signal to mechanical vibration fault signal, taking the local of impact fault detection in rolling bearing outer ring as an example, using the theory of Hertz elastic collision, when the rolling body through the local fault of the outer ring, the impact torque mechanical model of instantaneous and the large of amplitude are established. On this basis, the simulation model of the motor driven rolling bearing is established and carries on the simulation analysis. In order to obtain the actual motor stator current signal and the vibration acceleration signal of rolling bearing, the special rolling bearing fault simulation test bench is designed, and then the simulation results are compared and analyzed. The results show that the motor stator current signal can effectively sense the local fault of rolling bearing, and the impact torque mechanical model what had been established is al so practical.