Because of the lack of regulation ability of small hydropower and the significant seasonal impact on its power supply capacity, as well as the low controllability of photovoltaic in medium-voltage microgrid, the frequency stability of hydro-photovoltaic complementary medium-voltage microgrid in island operation is poor when the superior grid experiences a fault. With the purpose of promoting the frequency stability of the hydro-photovoltaic complementary medium-voltage microgrid, this paper proposes to improve the frequency control property of photovoltaic system, the virtual synchronous generator technology is applied to photovoltaic controller to control the medium-voltage microgrid frequency with small hydropower. Firstly, a detailed introduction to the mathematical model and control strategy of the power frequency controller and excitation controller for virtual synchronous generator technology. Secondly, the medium-voltage microgrid model, small hydropower model and photovoltaic model are analyzed. Finally, in PSCAD, a medium-voltage microgrid model with small hydropower and photovoltaic is built. The frequency stability of medium-voltage microgrid grid-connected to off-grid in dry season and wet season scenarios is simulated and analyzed, and the feasibility of water and photovoltaic participating in the frequency control of medium-voltage microgrid is verified.