In view of the chattering and weak robustness of sliding mode speed control for permanent magnet synchronous motor servo system, a speed control loop was designed by combining the improved integral terminal sliding mode surface with the generalized super-twisting algorithm. A piecewise sliding surface method was proposed to design an improved fast integration terminal sliding surface, by which the chattering problem could be significantly improved.An improved generalized super-twisting controller was designed as a switching control, by which the dynamic characteristics of the system could better improved. Finally, the stability of the algorithm was proved. The simulation results show that this method has the advantages of strong chattering suppression, fast convergence and good tracking performance.