In order to improve the current utilization and robustness of the motorized spindle,based on vector control,the plug in permanent magnet synchronous motorized spindle was studied.The fourth order equation of the maximum torque current ratio control was processed in normalization,and the equation was approximately solved by fitting the curve.The speed range of the spindle was expanded by using field weak magnetic speed regulation.The spindle speed was estimated by sliding mode observer.In order to overcome the chattering problem of traditional sliding mode observer,the Sigmoid function was introduced into the traditional sliding mode observer,the stability of the proposed strategy was deduced and explained by Lyapunov criterion.The high-speed grinding motorized spindle FL170-20-15 in the laboratory was taken as an example,and a simulation experimental platform based on MATLAB was built by using the above algorithm for experimental verification,and the effect of the control strategy was analyzed.The experimental results show that the chattering phenomenon of sliding mode observation is reduced and the robustness of the control system is improved.