Aiming at the chattering caused by the traditional sliding mode control using the discontinuous sign function as the switching function, a sensorless vector control method based on an improved sliding mode control with variable structure for the permanent magnet synchronous motors is proposed, so as to improve the static and dynamic performance of the system. Firstly, a control system with variable structure based on an improved sliding mode controller (ISMC) and an improved sliding mode observer (ISMO) is designed. Secondly, a continuous switching function, hyperbolic tangent function, is used as the sliding mode switching function, and its shape coefficient is adjusted by fuzzy logic control to reduce the chattering caused by the fixed boundary layer thickness. Then, the stability of the control system is proved by utilizing Lyaplov's second theorem. Finally, compared with other methods, the simulation results verify the feasibility and effectiveness of the proposed scheme.