In view of an improvement of the control performance of permanent magnet synchronous motors and a solution to the problems of chattering and slow response in traditional sliding mode control (SMC), a new sliding mode observer using a piecewise power function has thus been proposed. By adopting Lyapunov stability criterion, the stability of the system can be proved, with a sliding mode speed controller designed before the new sliding mode observer, followed by a subsequent comparison with the traditional PI controller. The Matlab simulation and experimental results show that the control method of the new sliding mode observer combined with the sliding mode speed controller is characterized with a stronger robustness and faster convergence speed, thus exhibiting an improved ability in suppressing system chattering. The results verify the effectiveness of the proposed method.