Power oscillation has always been a stability issue that needs to be solved in power systems. Study on large scale photovoltaic(PV) with energy storage suppresses power system power oscillations conforms to the current development direction of energy. First, the model of two-stage PV with energy storage grid-connected is established, and then the control strategy to suppress power oscillation is designed. The physical significance of the control strategy influencing the damping is derived using the damping torque analysis, and complex multi-machine system is analyzed using eigenvalue analysis. The simulation model of two-stage PV with energy storage connect to single machine and multi-machine system is built. The effectiveness of control strategy to suppress power oscillation is verified by time domain simulation and eigenvalue analysis. In multi-machine system, the effect of objective unit oscillation suppression is more obvious. The stability of the system is effectively improved.