Simultaneous perturbation stochastic approximation（SPSA） algorithm is proposed for tracing the maximum power of wind power system. It aims to enable system to be free from outside interference under variable wind speeds， and to maintain wind turbine at the maximum power operating point. For SPSA algorithm， wind turbine speed is indirectly controlled through adjusting the duty cycle of the power converter， which will enable wind power system to operate at the maximum power point under any wind speed， and do not need tachometer and anemometer in practical application. As shown in the simulation results， no matter how the wind speed changes， SPSA algorithm can effectively improve the power output of wind power system， and maintain the tip speed ratio（TSR） and coefficient power（CP） at the neighborhood of the optimum value.