Abstract: An adaptive robust controller based on non-linear backstepping method is developed for permanent magnet synchronous motors (PMSM) servo system with unknown parameters and load torque and other uncertainties. Other uncertainties including modeling errors and outside interference are considered in the system model, and then robust feedback control is added to inhibit influnce of the uncertainties on system performance effectively and realize high accuracy position tracking for PMSM system. It can be ensured by theoretical analysis that the position tracking error converges exponentially. Simulations show that the proposed method has better robustness and control accuracy than traditional adaptive backstepping control.