The mechanical simulator method is proposed as a speed sensor-less vector control method in a ultra-low speed region. In this method, an error between the calculated rotor frequency and the actual rotor frequency occurs when the set value of disturbance torque is different from its actual value. The error of the calculated rotor frequency causes to increase the slip frequency, which reduces the rotor flux. This results in decreasing the motor torque. To cope with this problem, the torque current error is compensated by PI controller and its output compensates the disturbance torque in the mechanical simulator. The proposed method is verified by both numerical simulations and experimental tests with a scale-downed experimental system.