The randomness and volatility of the output power of photovoltaic generator sets affect the safe and stable operation of the power supply system. In order to improve the frequency stability of the hydropowerphotovoltaic power supply system, the mathematical model of the hydraulic turbine speed control system is analyzed, then the optimization ability of the seagull algorithm and the reasoning ability of the fuzzy control are combined, and a seagull-optimized fuzzy PID control (SOAFPID) based method is proposed. The hydroelectric unit control strategy enables the system to quickly adjust the frequency deviation caused by photovoltaic and load fluctuations. The Simulink simulation model is built, the frequency stability capability of the system under different disturbance conditions is analyzed. The simulation results show that the hydroelectric unit controlled by SOAFPID has a minor overshoot and faster stabilization speed under photovoltaic and load power disturbance compared with the traditional PID control method. The dynamic regulation in the hydropower-photovoltaic power supply system performs well.