When the load phase angle is equal to the angle of the current disturbance, a detection method based on the alternate current disturbance (ACD) is used to detect islanding. However, the injected disturbances have a serious influence on the quality of output current. Therefore, combined with an improved active frequency drift method, an improved islanding detection method based on the alternate active frequency drift is proposed. The proposed method injects a different current distortion into current waveform in the adjacent period. The disturbance makes the frequency of the voltage at the point of common coupling (PCC) shift up in the first period, and shift down in the next period. Islanding is detected by judging whether the error of the frequency at the PCC in adjacent period changes alternately in the form of the positive and negative signs. The proposed method is validated by theoretical analysis and Matlab simulation. The results verify that the proposed method can identify the islanding accurately from non-detection zone, and the injected disturbances have less impact on power quality.