A sensorless control algorithm for surface PMLSM was designed. To overcome the drawback that the stator′s back EMF was too low to observe at low speed, an integral mathematical model of stator voltage was established in stationary reference frame axes, and the back EMF observation term was decoupled into an integral term with fixed amplitude and could be easily measured. Because of the influence of observation noise, the burr phenomenon of velocity signal obtained by traditional direct calculation method was serious. This algorithm used phase locked loop technology (PLL) to extract rotor position and speed signal. The secondorder frequency domain mathematical model of PLL was established to analyze its steadystate performance, and the dynamic tracking ability of PLL was discussed in the presence of phase jump, frequency step and frequency ramp of input signal. The simulation results showed that the algorithm could realize accurate observation of the rotor position and speed, and the control system had good stability and controllability.