With the improvement of intermittent energy such as photovoltaic in new energy grid, the disadvantages of low inertia and poor stability of the high proportion of new energy grid become more and more obvious. According to the characteristics that the synchronous motor-generator pair (MGP) can provide a large moment of inertia and is beneficial to the stability of the power grid, also by considering that the intermittent energy is unable to modulate frequency at the maximum power output, this paper proposes to introduce the energy storage system into the photovoltaic grid connected system via MGP, so that the ability of photovoltaic to participate in grid frequency modulation can reach the level of traditional thermal power units. A simulation model including thermal power unit, photovoltaic power generation, energy storage, MGP and load is built. By applying disturbance to the simulation model, the frequency modulation capability of MGP and energy storage participating in the new energy grid is studied. The results show that this method can effectively enhance the frequency support ability of the system and is conducive to the stable operation of the power grid.