Aiming at the problem that local island detection has a large detection blind spot or damages the power quality to a certain extent, this paper proposes a V2G discharge island detection method based on interharmonic impedance. First, the characteristics of electric vehicle charging and discharging station island detection are analyzed, and then a model is built based on the island detection principle of interharmonic impedance, and finally a simulation verification is performed. The experimental results show that this method can detect and handle the power island phenomenon in time in the case of power outage or network disconnection, ensuring the stable operation of the power grid and electric vehicle system.