In order to study the influence of stator auxiliary slots on the internal loss distribution of permanent magnet synchronous motors, a 50 kW surface-mounted permanent magnet synchronous motor is taken as an example. Starting from the basic theory of electrical machinery and electromagnetic field, combined with the finite element theory, according to the actual structure of the motor with one pole as the solution domain, a two-dimensional electromagnetic field mathematical model and physical model are established. The finite element method is used to numerically calculate the two-dimensional electromagnetic field of the permanent magnet synchronous motor, analyze the influence of the auxiliary slot width and groove depth on the magnetic field distribution in the motor, and then explore the iron loss and permanent magnet eddy current loss of the stator core of the motor when the auxiliary slot is opened. The distribution characteristics of stator copper loss and total loss provide a theoretical reference for permanent magnet motor design.