In order to obtain a motor with high efficiency, good starting performance and stable operation, an improved multiobjective particle swarm algorithm is introduced to optimize a threephase fourpole asynchronous starting permanent magnet synchronous motor （PMSM）. Based on the structural characteristics of the PMSM, a mathematical model is established. The length of the core, the number of conductors per slot of the stator, the size of the stator slot and the size of the permanent magnet are selected as optimization variables, and the efficiency, power factor, starting current multiple, starting torque multiple and the outofstep torque multiple are the optimization targets. An electromagnetic calculation program is written with MATLAB.By combining the improved multiobjective particle swarm algorithm with electromagnetic calculation program, the efficiency, power factor and starting performance of the motor are optimized. Through the analysis of the optimization results, it is shown that the optimization has achieved the expected results under the premise of meeting the requirements of other performances. The effectiveness of the algorithm is verified.