The rotor speed of DFIG(doubly fed induction generator) and system frequency are decoupled, this leads to poor responding performance of DFIG to the change of power system frequency. The rotary inertia and primary frequency control ability are decreased with wind power penetration growing continuously. In order to reduce the negative impact of wind power on system frequency, a variable parameters primary frequency control loop based on the conventional decoupling control is proposed in this paper. The factors influencing the performance of the control loop are analyzed, which including the gain of the control loop and wind speed. Based on that, the gain of the control loop is adjusted along with the change of wind speed and the size of power imbalance. The simulation result in matlab/simulink with the example of IEEE 9-bus system incorporated wind farm demonstrates the effectiveness of the proposed control strategy.