Abstract: A fault-tolerant paralleling active power filter (APF) is proposed. Its structure and running models are given. The fault structure of the inverter based on three-phase four-switch structure and work principle when the inverter of APF has faults in some phase is analyzed. The method to stabilize the DC-link voltage is proposed. The control strategy for APF working on both normal state and fault state is proposed. The simulation results show that harmonic currents are suppressed by the fault-tolerant paralleling APF whether working on normal states or fault states, and the DC-link voltage stay stable and the system has high reliability.