Islanding detection technology is essential for micro-grid which is required that it must work at grid-connected and islanding modes .With regards to this ,an islanding detection method ,which add positive power disturbances on the reference active power to make inverter frequency deviate out of normal range when grid is going wrong ,is presented. On this basis ,add frequency positive feedback to the coefficient by judging continuous times of frequency deviation to give corresponding disturbance to improve the selection of active power disturbance ,which can accelerate the speed of islanding detection and reduce the impact on power quality when grid is in the normal state .In the meanwhile ,an program which islanding detection algorithm is applied in micro-grid by analyzing its structure characteristics .At last simulation results show the effectiveness of islanding detection algorithm.