In this paper, the parallel active power filter is taken as the research object. A diode-clamped three-level topology is used as the main circuit of the system. A voltage space vector pulse width modulation (SVPWM) algorithm based on a 60°coordinate sys- tem is proposed, which simplifies the operation process of the traditional three-level space vector algorithm. The reason for the po- tential fluctuation of the neutral point in the three-level topology is analyzed. In the non-orthogonal coordinate system, the DC-DC conversion technology is used to realize the balance control of the neutral point potential. The system simulation model is estab- lished in Matlab / Simulink environment. The simulation results show that the system has better harmonic suppression ability, which verifies the feasibility of the scheme.