Active Frequency Drift (AFD) Method is a simple and effective islanding detection method. However, the power quality is affected due to the introduced distortion on inverter current and the non-detection zone is bigger. This paper proposes an improvement to AFD by adopting positive feedback of voltage frequency and changing part of the current amplitude rather than changing the current frequency directly. The total harmonic distortion is analyzed and non-detection zone of the improved algorithm is described by using coordinate plane. Analysis and simulation show that compared to traditional method, the improved one has less distortion on inverter current, smaller non-detection zone and better power quality.