In view of the special structure of isolated grid, the backtracking algorithm which is widely used in black-start path optimization has its defect, such as time-consuming and blind optimizing. In this paper, minimal spanning tree integrated with backtracking algorithm is proposed to realize the path optimization for black-start. Firstly, this paper builds the weight factors of transmission line and unit to identify significant nodes. Then, the optimal black start topology is built with the maximum weight factors of transmission line. After that, backtracking algorithm is introduced to calculate the specific black-start path from the optimal tree topology, where the target is to maximize the weight factor of path. The optimization algorithm can effectively reduce the path search space and has high robustness. Finally, New England to-Unit 39-Bus System is used as an example to verify the effectiveness of the proposed algorithm.