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In this paper, a multi-objective feedback nonlinear sliding mode control strategy is designed to reduce the impact of the disturbance on the hydro-generator set in the tailrace tunnel with a sloping ceiling, aiming at ensuring the safe and stable operation of the hydro-generator set under severe electrical and hydraulic conditions. Firstly, according to the actual hydraulic structure of a hydropower station with a tailrace tunnel with a sloping ceiling, a comprehensive model of a nonlinear hydro-generator set with excitation control and guide vane opening control is established. Secondly, according to the design method of multiple objective feedback control law and the principle of sliding mode control, the paper establishes a standard matrix of Brunovsky foundation for accurate feedback linearization by selecting control targets of turbine flow, guide vane opening, active power, speed, and terminal voltage, designs the sliding mode control system, and finally obtains the general nonlinear control law through nonlinear transformation. Simulation results show that, compared with PID control and Multiple-index Nonlinear Control (MINC), the Multi-objective Feedback Nonlinear Sliding Mode Control (MOFNSMC) in this paper has a faster recovery capability and good disturbance-resistant capability with a small oscillation amplitude of the hydro-generator terminal potential in the case of electrical disturbance. In the case of hydraulic disturbance, it can effectively reduce the overshoot and the number of oscillations of the turbine waterhead and the flow and the water hammer pressure on the hydraulic structure, to improve the safe and stable operation of the hydro-generator set.