Islanding detection is a mandatory feature for grid-connected microgrids. Conventional passive islanding detection methods suffer from the existence of non-detection zone， while active islanding detection approaches are devastating to microgrid. To realize the detection of the non-detection zone and devastating， a novel islanding detection method based on positive feedback of voltage harmonic distortion is proposed. According to the IEEE Std 1547， theoretical analysis and simulation tests are conducted. The results indicate that the proposed method is able to detect islanding rapidly and effectively in the case that voltage and frequency are within normal limits. Also， this method is effective when single-phase and two-phase of breaker are disconnected. Furthermore， trip on false islanding can be avoided. The method achieves the goals of islanding detection without devastation and non-detection zone.