A discharge strategy for a battery-supercapacitor hybrid energy storage system is designed based on model predictive control theory to match the power and energy requirement of the magnet coil of HL-3. Using toroidal field coil as the load of the energy storage system, the mathematical model of the system and the objective function based on battery/supercapacitor characteristics and energy demands of the load is established. The optimal switching sequence is solved in real time. Long cycle control is applied on battery energy storage system to achieve stable discharge of the battery, while short cycle control is applied on supercapacitor energy storage system to achieve transient response of the supercapacitor. Simulation experiments are conducted using MATLAB/Simulink. The hybrid energy storage system stably outputs a flat top current that meets the load demand, with a current ripple of 0.22%. The simulation results verify the effectiveness of the proposed control method.