A partition and island identification method is put forward for the smart distribution network based on the reachability matrix.By using the topological structure of the distribution network，the adjacency matrix is formed first to describe the distribution network diagram.Based on the adjacency matrix，we can get the reachability matrix，which contains node connectivity information and network partition information.On this basis，the switch property vector is defined.Using the corresponding elements in the above matrix for logical AND operation we can obtain the regional property vector and then quickly judge each regional property，whether the island exists or not and the number and range of islands.Results of example analysis have verified the accuracy and feasibility of the method proposed.