Abstract: For the island partition of distribution network considering the output fluctuation of distributed generators（DG）and load uncertainty,a new optimal island partition model and its solving method are presented based on tree knapsack problems（TKP）.The basic idea of the paper is first,a new stochastic island partition model considering the uncertainty of DGs and loads is developed.Then the Latin hypercube sample method,the deterministic tree knapsack algorithm and mathematical statistics method are adopted to determine the composition of the initial island,including DGs and loads.Finally,for each initial island,the stochastic optimal power flow is used to optimize and adjust the initial island on the basis of island reconfiguration.Through the above optimization and adjustment,the security,optimization and economy for each DG island operation are ensured.The method has achieved optimal islanding under the uncertainty of DGs and loads,the islands most likely to appear according to the real-time situation,which has a stronger credibility compared with the condition of certainty.The results of an PG＆E 69-bus distribution system with several DGs show the validity of the proposed model and method.