Abstract: Aiming at the problems of steady-state error and large buffeting degree in the speed control system of permanent magnet synchronous motor (PMSM), a new frit-order sliding mode speed controller was designed to replace the traditional sliding mode speed controller. By studying the theory of fraction-order control and combining with the general exponential approach rate function, a new fraction-order approach rate is designed, and the traditional sign function is replaced by arctangent trigonometric function. The extended state observer is used to estimate the total disturbance error of the system and obtain accurate rotor velocity information. Lyapunov stability criterion is used to prove the feasibility of the scheme. Finally, under the same motor parameters, a simulation model was built and simulated according to the PMSM system control block diagram, and the performance indexes of the traditional sliding mode control were compared. The experimental results show that the motor system with the new fractional sliding mode controller can respond quickly, improve the anti-interference ability, and the system stability and robustness are better.