The risk of sub-synchronous oscillation of PV grid-connected system is increased by the decrease of power grid strength or the disturbance of DC voltage. It is theoretically necessary and engineering urgent to study the mechanism of sub-synchronous oscillation of PV grid-connected system and put forward corresponding suppression strategies. In this paper, a dq synchronous rotating coordinate system control model of PV grid-connected system with subsynchronous oscillation is established, and the influence of subsynchronous oscillation on PV grid-connected system is analyzed according to the model. An adaptive SSO suppressor based on SVD-Prony algorithm is designed to track and suppress sub-synchronous oscillations that vary in each frequency band. This algorithm can extract the effective mode information of the subsynchronous oscillation in PV grid-connected system, and then update it to the central resonant frequency of the suppressor, and generate the output which can compensate the subsynchronous oscillation component in the closed-loop control system. Finally, a simulation experiment platform is set up to verify the effectiveness of the suppression strategy proposed in this paper.