In order to improve the sinusoidal level of air gap magnetic field of the traditional surface PMSM, reduce its harmonic losses and fully reflect its energy-saving advantages, this paper introduces a type of sinusoidal pole width modulation permanent magnet synchronous motor. The surface magnetic poles of the rotor iron core constitute by a number of small array magnets, which makes the air gap magnetic field more sinusoidal. Placing starting winding in remaining space between array magnets of rotor outer surface to make surface-mounted permanent magnet synchronous motor add self-starting function. The sine wave distortion rate of air gap magnetic field of sinusoidal pole width modulation structure was compared with traditional surface-mounted structure by electromagnetic field calculation and experiment. The copper starting winding and aluminum starting winding were placed in sinusoidal pole width modulation structure motor respectively, and then the paper analyzes dynamic torque and rotational speed of self-starting progress. Finally the analysis is verified by experiments.