Abstract: In view of problem of low computation efficiency and poor generality of existing evaluation method of coal mine power grid, an improved BFS-the minimal path evaluation method was proposed. The method uses the breadth-first search method to quickly solve division optimization model of distribution network island, and then adopts the minimal path evaluation method to evaluate reliability of power supply according to the operation scope of island. The experimental results show that the method improves evaluation speed of weak links of power grid, and evaluation results are safe, reliable, accurate and effective.