Abstract: A novel optimal island partition model of the distribution system with distributed generation（DG） is proposed and a two-stage method based on branch and bound algorithm is applied to this model.Firstly,an initial optimal island partition scheme is acquired through island isolating process composed of a number of tree knapsack problems（TKPs） and island combination process;and then a feasible island partition scheme is finally obtained after the rationality checking and adjusting of the initial scheme.Each TKP is solved by a branch and bound algorithm.Since the load priority,controllable/uncontrollable load,and the restrictions of power balance,voltage and equipment capability are all taken into account,therefore,the proposed model and method meets the demand of the practical engineering very well.Moreover,the computational complexity of the algorithm proposed is relatively low.The results of the samples demonstrate the validity of the new model and method.