Abstract: In the development project of the first demonstration device for proton therapy in China, the injection and extraction magnet power supplies of proton accelerator were realized in parallel mode of module current source, but the small inductance of injection and extraction magnet is not conducive to the noise from switch in power supply. In order to meet the needs of the project, a phase shift design scheme was proposed and the ripple normalization magnitude of the 3-phase shift was deduced, which theoretically verified the feasibility of the scheme. On this basis, the H bridge structure by MOSFET was used as the basic unit to realize the module power supply. The switch ripples of injection and extraction magnet power supplies meet the design and application requirements, and the feasibility of power supply topology was verified. Since operation, the three magnet power supplies have operated reliably and stably for more than 20 months.