In order to enhance the damping of power systems integrated with wind farms，a novel method for designing the additional damping control strategy of wind turbine-driven doubly-fed induction generator（DFIG）is proposed.Firstly，the concept of dynamic frequency character is defined and its calculation formula is deduced.Secondly，based on the concept of dynamic frequency character，the phase and amplitude conditions for wind farms to produce the positive damping effects on their connected power systems are proved.Based on the proved conditions，a damping control strategy is proposed on the basis of the conventional double closed-loop control structure.Finally，by means of Power System Analysis Software Package（PSASP），case studies on2-area and multi-area power systems show that the proposed control strategy can improve power system damping，while facilitating parameters tuning，debugging and engineering implementation.