The PMC system of PWR nuclear power plant is a servo control system based on PMSM permanent magnet synchronous motor. The traditional Clarke and park coordinate transformation theory algorithm is used for precise control. This paper analyzes the composition of the servo system of PMC loading and offloading equipment, the principle and control algorithm of PMSM permanent magnet synchronous motor, and studies the double closed-loop control model based on current sampling and position sampling, the protection function setting of servo system and the self-learning method of PMSM. The research results show that the PMC system adopts the double closed-loop control theory of field oriented control (FOC) with DSP as the control core. Through the close-loop cooperation of PLC, servo driver, PMSM permanent magnet synchronous motor and resolver, the precise control of speed loop and current loop is realized, and the three closed-loop is realized by the position loop of PLC Control. This study provides a reference for the realization of independent deep maintenance of PMC equipment, and provides theoretical support for the future transformation of PMC servo control system and fault prediction of servo system.