In recent years, the penetration rate of power electronic equipment in the system has gradually increased, and harmonic problems have become increasingly serious. Active Power Filters (APF) can output compensation currents with opposite phases to the harmonics of the power grid, thereby achieving the function of actively controlling harmonics. Therefore, the output current of APF has wide-band characteristics, and the traditional LCL output filter will attenuate the output wide-band compensation current. Based on this current situation, this article analyzes the working mechanism of the APF main circuit, compares the characteristics of different filter circuits through Bode plots, and then proposes a filter with coupled inductor and three-notch branch and its design process. The switching ripple problem of the wide-band compensation current in the APF was filtered out. Finally, through Matlab/Simulink simulation and experimental comparison, it was verified that this filter is more reasonable and effective than the traditional LCL filtering link.