This paper presents the design of a DC power amplifier based on the modular multilevel converter. The qualitative relationship between the submodule capacitance and the capacitor voltage ripple are analyzed. To attenuate the high frequency switching ripple in the output voltage of the DC power amplifier, two-stage LC filter is selected, with its parameters obtained according to the five-order Butterworth filter. Simulation results prove that the DC power amplifier can work in four quadrants and the two-stage LC output filter can attenuate the high frequency switching ripple as designed. Experiment results are given to verify the performance of the two-stage LC output filter.