Abstract: To analyze the influence of the active power output of direct-drive wind farms in weak grids on the subsynchronous oscillation (SSO), a dynamic mathematical model of the grid-connected system is established. Using the eigenvalue analysis and the participant factor calculation, the dominant oscillation mode and the main participating control link are obtained. By analyzing the relationship between the active power output and the SSO characteristics under different control parameters and system parameters, the reasons for different reviews on the influence of the active power output on the SSO damping in academia and engineering are illustrated, and the dominant factors influencing the relation between the active power output and the SSO damping is determined. Meanwhile, according to the relevant characteristics of the active power output and the SSO damping, a parameter adjustment scheme to suppress the SSO is developed to play an important guiding role in actual engineering. The time-domain results verify the correctness and validity of the relevant characteristics and parameter adjustment scheme.