Based on the fundamental principle of traditional magnetic circuit design, the simulation model of permanent magnet synchronous motor (PMSM) of canned pump is established by the ANSYS software. The load magnetic field of the motor is calculated. The magnetic field distribution of the motor is obtained. The performance of the maximum torque output under different number of magnetic pole pairs, the permanent magnets in different sizes and different rotor core thickness is analyzed in detail. The results of simulation provide theoretical foundation for the optimization design of this kind of motor.