Aiming at the characteristics of permanent magnet synchronous motor (PMSM) such as strong coupling and nonlinearity, we propose a fractional-order control scheme for the speed control of PMSM system based on the analysis of the fractional calculus theory. The simulation is conducted by using Matlab / Simulink. Simulation results indicate that the fractional-order PI controller can improve the disturbance rejection performance of the PMSM speed-adjusting system.