The invention discloses an island detection method based on voltage harmonic sequence components. A sliding data window is used to calculate the variation values, |delta U2(1)|, |delta U2(2)|, |delta U4(1)| and |delta U4(2)|, of positive and negative sequence components of the specific voltage subharmonic of a grid-connected inverter terminal, and whether islanding occurs is determined according to the variation values, |delta U2(1)|, |delta U2(2)|, |delta U4(1)| and |delta U4(2)|. The purpose is to detect the islanding effect quickly and effectively without affecting the power quality of a power system. The island detection method has the advantages of simple principle and wide application range, and islanding under various circuit breaking conditions and the most serious islanding conditions can be quickly and effectively detected.