Doubly fed induction generators（DFIGs） provide little active power response to frequency changes of power grid. Meanwhile， traditional DFIGs cannot regulate their active power to support the system frequency due to the operation of maximum power point tracking（MPPT）. DFIGs can be down-regulated through increasing wind generator rotor speed or adjusting pitch angle， thereby improving frequency regulation margin for power systems. However， in various operating conditions， overspeed control and pitch control both have limitations in real engineering application. In order to utilize the potential of DFIGs frequency regulation capability， this paper presents a frequency control strategy to coordinate overspeed and pitch controls. Depending on the wind speeds， the coordination strategy is composed of low， medium and high wind speed control modes and the correlated criterion is also presented. Simulations show that the system frequency stability can be improved by DFIGs based on the proposed control methods.