Active power regulation in a wind farm has become a fundamental requirement to mitigate the adverse effect on grid. Wind turbines even in a same wind farm have different generating capability due to the wind speed variations and operation conditions. An active power control scheme based on the state classification algorithm is presented. According to the estimated power in next power control cycle and operation status， the wind turbines are classified into different sets with different power adjusting margin. By this way， the whole wind farm active power control goal can be reached accurately and stably. Finally， the power control is applied to the actual power control in wind farms to verify the method.