Large-scale wind farms are generally integrated by long-distance transmissions, but power grids cannot sufficiently support the access point voltage of these wind farms. The access point voltage undergoes a stability problem under wind speed variations. However, the reactive power compensation device cannot reconcile the requirements of response speed and compensation capacity. Despite their fast power decoupling control, the reactive power capability of doubly fed induction generators is restricted by active power output. To satisfy the reactive power demand of system under wind speed variations, coordinating the reactive power capability and active power output of wind farm is the key solution, based on which a novel active control idea is proposed. The reactive power capability of wind farm and the reactive power demand of system are both studied, and the controllable conditions of access point voltage are analyzed. Active voltage control strategies, including active adjustment of reactive power reference, active speed control, and active pitch angle intervention according to wind speed ranges, are proposed. In the simulation, the method is verified to adequately consider the reactive power demand, and excavate the wind farm reactive power capability. The method also effectively suppresses the change of grid voltage under wind speed variations.