The invention provides an island dividing method and a device for a power distribution network. The method comprises the steps of determining the topological structure of the power distribution network according to the power supply relationship among each distributed power supply and each user in the power distribution network, wherein the distributed power supply and the user are both nodes in the topological structure; simplifying the nodes of the determined topological structure; dividing islands of the simplified topological structure according to an intelligent water droplets algorithm integrated with the equivalent electrical distance to obtain a plurality of islands; verifying and correcting the plurality of obtained islands to determine a final island division scheme. According to the technical scheme of the method and the device in the invention, the equivalent electrical distance is integrated, and the factors of electrical distance, impedance and the like are considered. Therefore, the characteristics of a power system are fully embodied.