Abstract: The involvement of wind turbine in the electromechanical oscillation mode of a synchronous generator after the supplementary active control makes the system power oscillation characteristics more complex, which is not conducive to the design of the supplementary active power control parameters. In order to study the effect of supplementary active control of wind turbines on system stability, firstly, we established a small-signal model of the dynamic action of the wind turbine and synchronous generator after considering the characteristics of the phase-locked loop, analyzed the influence of the supplementary active power control on the stability of the system oscillation based on this model using the damping torque method, and proposed a design method for the supplementary active power control parameters in which the equivalent inertia time constant and the damping ratio of the system were taken into consideration. Finally, the influence of each factor on the system's low-frequency oscillation stability was quantified by the simulation recults of the 10-machine 39-node system. The results show that the reasonable setting of the supplementary active power control parameters, the filtering time parameters and the phase-locked loop bandwidth of wind turbines can improve the frequency stability of the system. The validity of the theoretical analysis is further verified.