In order to design a V-shaped built-in permanent magnet synchronous motor with good starting performance and more stable operation, the no-load back electromotive force （EMF）, air gap magnetic density, cogging torque and torque ripple are optimized by improving the structure of air magnetic isolation tank. Taking the geometric parameters of the air magnetic isolation tank as the variables to be optimized, the Latin hypercube sampling algorithm is used for multi-objective optimization to obtain the optimal parameter combination. After optimization, cogging torque decreased by 45%, torque ripple decreased by 4.4%, and electromagnetic torque increased by 5.2%. The optimization result is ideal, verifying the rationality of the optimization scheme for the permanent magnet synchronous motor.