Abstract: In order to improve the energy efficiency of the hydraulic injection molding machine, a permanent magnet synchronous motor for the injection molding machine is designed to transform the servo system of the injection molding machine. Combined with the actual production conditions of the injection molding machine, the main dimension parameters of the permanent magnet synchronous motor used in the injection molding machine were determined, and the finite element model was built using Ansys Maxwell 2D software. The article focuses on the selection of the slot combination, analyzes and designs the rotor structure, and proposes that the cogging torque of the “1” magnet built-in permanent magnet motor can be effectively weakened by a combination of inhomogeneous air gap and pole arc coefficient optimization methods. . According to the design parameters of the prototype, the design value and the experimental value of the error is small, the motor used in injection molding machine servo system transformation, and achieve better energy-saving effect.