In this paper, the two-stage photovoltaic grid connected power generation system is taken as the research object. By analyzing the different inertia control functions on both sides of photovoltaic boost and inverter, a coordinated control strategy is proposed, and the influence of different parameters on the system inertia is analyzed by establishing the static synchronous generator model of the system. The results show that the virtual inertia of the two-stage photovoltaic grid connected power generation system mainly comes from the photovoltaic reserve capacity and the DC capacity of the inverter side. When the photovoltaic side responds to the grid frequency fluctuation, the lowest point of frequency drop is improved, the steady-state deviation of grid frequency becomes smaller, and the larger the sag coefficient is, the more obvious the improvement effect is, but the change rate of frequency does not change. When the inverter side responds to the grid frequency fluctuation, the grid frequency change rate becomes smaller, and the larger the droop coefficient is, the more obvious the improvement of the frequency change rate is, but the steady-state deviation of the grid frequency does not change. The coordinated control proposed in this paper makes good use of the advantages of the two response frequency fluctuations, so that the frequency change rate, the lowest point of frequency drop and the steady-state deviation of frequency are significantly improved, and the effect of frequency fluctuation suppression is the best.