Water-cooled resistive high-field research magnets require a high power supply with an extremely high current stability, and a low current ripple and noise. The conventional resistive magnet power supply uses thyristor rectifiers, followed by a passive filter and an active filter in series to reduce the voltage ripple. This Paper describes a new circuit topology design of the resistive magnet power supply, which consists of an uncontrolled rectifier bridge and a three-level buck converter in series instead of the conventional thyristor rectifier. The three-level buck converter works at a higher switching frequency, which can greatly reduce the cost, volume and weight of the filter. According to simulation and analysis results, it is seen that the three-level buck converter structure provides a lower voltage and current ripple than the conventional thyristor rectifiers, reduces the voltage stress of the power electronic devices. Beside, without power factor correction devices, this new design can achieve a higher power factor.