Because of sharp speed fluctuations under low frequency, this paper proposes an integral sliding mode variable structure control strategy for single-rotor permanent magnet synchronous motors. With regards to the periodic fluctuation of load torque of single-rotor PMSM, a full-dimensional torque observer is designed to observe the load torque, and the observed values are fed back to the integral sliding mode controller. The simulation results verify that the torque observer can measure the load torque variation and the integral sliding mode variable structure control can effectively suppress the speed fluctuation of the single-rotor PMSM at low frequency.