In the design of a power supply powered by energy storage system with a battery pack to drive laser diodes with BUCK chopper circuit for constant current and step-down voltage，Personal Simulation Program with Integrated Circuit Emphasis(PSPICE) models，which of components such as the battery pack, laser diodes in series, and of system with a closed loop are constructed. Parameters of output inductances and capacitors for filtering circuit are determined by simulations as well as the optimized parameters of the Process Identifier(PID) to realize stability of the closed loop. The stability of the power supply is studied by simulation under different conditions. The results indicate that a constant current power supply made by this technology could output more than 100 A current and 230 V voltage with less than 3% ripple.