Abstract: The paper analyzed working principle of active power filter, derived mathematical model of single-cycle control of three-phase three-wire active power filter. It combined digital single-cycle control and ip-iq harmonic current detection method to realize control of active power filter. Compared with traditional single-cycle control method, the proposed method retains advantages of good real-time performance and robustness, meanwhile cancels the integrator, and reduces complexity of the single-cycle control circuit. The proposed method was simulated using Matlab/Simulink software and validated by experiment platform with DSP as the core, and the results of simulation and experiment prove feasibility and effectiveness of the method.