Since passive islanding detection methods have non-detection zone and traditional active frequency drift（AFD） methods may cause active current fluctuation， an improved AFD islanding detection algorithm is proposed. The algorithm realizes current frequency drift by controlling reactive current， so as to achieve positive feedback of voltage frequency at the point of common coupling（PCC） in islanding state and realize anti-islanding function. To reduce reactive current injection to the power system， the improved AFD algorithm should be combined with traditional passive islanding detection algorithm. Simulation and experiment results show that the improved algorithm can not only eliminate the non-detection zone of passive islanding detection algorithms when the loads power and the inverter power match， but also overcome the active current fluctuation of traditional AFD algorithms and improve the stability of DC bus voltage.