The island operation is a new operating mode of the distribution network after the distributed generation is introduced. And it is a beneficial supplement for the operation of the distribution network. The distributed power supply capacity is made full use to ensure the safe operation of the maximum number of significant load when the fault occurs. A combinational algorithm of the planned island partition is presented according to the principle of power balance in the distribution network failure. Heuristic search strategy and the breadth-first search algorithm are adopted by taking into account the characteristics of different types of distributed power. The validity of the method is proved by the example.