Islanding effect is one of the basic problems of photovoltaic grid-connected systems that must be resolved. Against the traditional active phase-shifting islanding detection method which has the problems of non-detection zone and a greater influence on the output power quality, by analyzing the relationship between the parameters and the non-detection zone of traditional detection method, and based on the fuzzy control, this paper proposes a novel active phase-shifting islanding detection method. The parameter k of the method is adjusted adaptively according to the change situation of frequency of voltage at the point of common coupling when the islanding occurs. Matlab/Simulink simulation results demonstrate the method not only can detect the islanding accurately and quickly, but also reduce the non-detection zone, and at the same time reduce the impact of disturbances to power quality. The inverter output current distortion is reduced by 0.48% compared with the traditional method.