To accelerate the reliability evaluation of large-scale complex distribution networks, an improved algorithm based on secondary node optimized numbering is proposed. Firstly, the node is numbered sequentially to improve the search efficiency. Then a virtual node is added in each branch, which can eliminate the impact of switch type in both ends of the branches and reduce the required memory. Finally, the distribution network is represented in sections according to the switch type in the branch. And the failures are enumerated based on section as a unit. The optimized numbering of the section can avoid the repeated work in deep-first search for the front circuit breaker. As a result, the time cost of searching is significantly reduced and the computation efficiency is improved. Meantime, the occupancy rate of CPU is also reduced. The RBTS-BUS6 test system and an actual large-scale complex distribution network are used to verify the accuracy and effectiveness of the proposed method and its high practical value of engineering.