Abstract: Islanding operation of distribution systems with distributed generators（DGs）is able to fully enhance the availability of distributed energy and reliability of power supply.A novel islanding model of distribution systems with DGs is proposed,in which the directed graph model is used.First,two new concepts,one of virtual node and the other virtual demand,are introduced to build the distribution network structure model with alterable branch direction,so that the feature of distribution systems that it operates in dendroid mode can be guaranteed by the proposed distribution network structure model.Then,a novel islanding model of distribution systems with DGs is proposed with tie switches operability,the load priority and controllability and operation characteristics of DGs considered.The proposed islanding model is converted as a mixed-integer linear programming problem for easy solution.Finally,a modified PG＆E 69-bus system is used for demonstrating the effectiveness of the proposed island partition strategy.