Abstract: In the vector control system of surface-mounted permanent magnet synchronous motor (SPMSM), the speed- related voltage coupling term introduced by coordinate transformation degrades the control performance. The conventional complex vector regulator suffers from incomplete decoupling, slow dynamic response and insufficient robustness under parameter perturbations and external disturbances. To solve these problems, an accurate discrete mathematical model of SPMSM is established, and a discrete sliding mode composite current control strategy based on direct design method is proposed. The complex vector current regulator obtained by direct design is used as the main controller to realize current decoupling under the ideal motor model. The discrete sliding mode current regulator is adopted as the auxiliary compensator to suppress the effects of parameter perturbations and load disturbances. Simulation and experimental results verify that, under parameter mismatch conditions, the proposed strategy reduces dq-axis current coupling fluctuation by more than 60%, increases dynamic response speed by 30%, and shortens the adjustment time by 40%, which significantly enhances the system robustness and stability, and has practical engineering value.