This paper presents a novel maximum power point tracking (MPPT) control strategy for direct-driven permanent magnet synchronous generator (PMSG) based on wind energy conversion systems (WECS). Considering wind energy’s drastically nonlinear and uncertainty features, the proposed control strategy adopts wind turbine’s optimum tip speed ratio (TSR) tracking algorithm to achieve maximum energy conversion efficiency, and implements an extended state observer (ESO) of the wind turbine aerodynamic torque with an adaptive sliding mode control (SMC) method to realize high tracking performance for the optimum TSR. The integral term in the sliding mode surface function can ensure the TSR tracking control without steady error. The wind turbine aerodynamic torque can be evaluated exactly by the ESO which increases the determinacy of wind power disturbance in MPPT control system. Due to the new reaching-law algorithm designed by power combination function and optimum speed tracking error negative feedback loop, the gain of the switch function is granted the capability of automatic adjust with TSR tracking error, and the chattering amplitude can be progressively damped. Simulation results show that the proposed controller has a better stability, adaptability and robustness compared with that of intelligent PID controller.