The invention provides an island detection method based on binary tree complex wavelet transformation, and belongs to the field of electric power systems. The island detection method comprises the following steps of acquiring control variables of a three-phase voltage type inverter, and establishing a PQ decoupling control mathematical model of a grid-connected inverter based on the acquired control variables; acquiring electrical change characteristics of a public connection point of a microgrid island under a power matching condition according to the established PQ decoupling control mathematical model; extracting voltage and current harmonic signals at the common connection point by means of a wave trap, decomposing the voltage and current harmonic signals based on binary tree complex wavelet transformation to construct a characteristic vector corresponding to the micro-grid; and improving a support vector machine on the basis of a support vector selection and genetic algorithm, andadopting the improved support vector machine to identify the island state of the microgrid. By virtue of improvement of the support vector selection and genetic algorithm, damage of the active detection method to the electric energy quality can be eliminated, and the problem of detection blind areas existing in the traditional passive detection method also can be solved.