A fractional-order modeling approach for a permanent magnet synchronous motor speed servo system is proposed applying a method combining electromagnetic part modeling and mechanical part modeling. Based on the proposed fractional-order model and system identification scheme, system identification experiments are performed on the electromagnetic part and the mechanical part of the permanent magnet synchronous motor speed servo system, respectively. The fractional-order model parameters of these two parts are identified with these experimental results, and the fractional-order model of the permanent magnet synchronous motor speed servo system is integrated from these two parts. Simulations and experiments in open-loop and closed-loop are performed based on the obtained fractional-order model and integer-order model. The advantage of the proposed fractional-order model for the permanent magnet synchronous motor speed servo system is demonstrated by the simulation and experimental results.