To address issues such as power oscillation and frequency overshoot in the grid-connected photovoltaic and energy storage system operating at virtual synchronous generator (VSG) mode that has fixed rotational inertia, an adaptive control strategy for VSG in the grid-connected photovoltaic and energy storage system is proposed. Firstly, a model of the grid-connected power generation system which on basis of VSG control and containing photovoltaic and energy storage is established. The front stage of the grid-connected power generation system adopts photovoltaic MTTP control and energy storage control. Then, the influence of rotational inertia on the dynamic characteristics of VSG is analyzed according to characteristic curves of the power angle and the rotor angular frequency. The RBF neural network is applied to the VSG to adaptively adjust the rotational inertia. Simultaneously, based on a fixed damping ratio, the damping coefficient is adaptively adjusted as the rotational inertia changes. A simulation model about the adaptive control of VSG for the grid-connected photovoltaic and energy storage system is built in MATLAB/SIMULINK to verify the feasibility of this control strategy. Finally, a comparison between the adaptive damping control strategy for rotational inertia and other control strategies is conducted. Simulation results demonstrate that this control strategy can suppress active power oscillations in the grid-connected photovoltaic and energy storage system and improve rotor angular frequency overshoot.