Abstract: In order to reduce the output current ripple of the accelerator DC excitation power supply, a DC active filter (DAF) for suppressing output current ripple of power supply was studied. Using the method of detecting the load voltage, the problem that the current ripple amplitude is very small and difficult to detect was solved. The objective voltage ripple was reduced by controlling the DAF to inject or absorb harmonic current, and the purpose of reducing the current ripple was achieved. The buck/boost circuit was designed as the main circuit of the active filter, which can maintain the stability of the storage capacitor voltage and eliminate the rectifier circuit. The design was simulated and an experimental prototype for verification was built. The experimental results show that the designed DAF has a certain suppression effect on low frequency ripple.