Abstract: In order to improve stability of sensorless control for interior permanent magnet synchronous motor of mine-used electric locomotive at low speed stage, an improved pulsating high-frequency voltage injection method was proposed. High-frequency sinusoidal voltage signal is injected into direct axis of estimated synchronous rotating coordinate, and high-frequency current of quadrature axis is processed through low pass filter, so as to obtain signal containing estimation error of rotor position angle. The signal is input into Luenberger observer to calculate estimated rotor position. The simulation and experimental results show that the method can estimate rotor position angle and speed accurately at low speed stage, so that electric locomotive can realize smooth starting, operation and stopping at low speed stage.