According to the basic aerodynamics theory, the principles of maximum power point tracking (MPPT) were analyzed for the PMSG wind turbine system in this paper. The equivalent control and state equations of sliding mode motion on the switching surface were derived based on the known characteristics of wind turbines and variable structure control theory. In order to weaken the chattering of sliding mode control, a method of fuzzy tuning quasisliding mode control (FQSMC) for the MPPT was presented. The gain coefficient of switching control was tunned online according to the system state. Moreover, a Lyapunov based closedloop stability analysis was discussed and a sufficient condition for asymptotic stability was obtained. Finally, the system model was built and simulation results were compared with those of the PID method, which showed the effectiveness of the proposed control strategy.