In order to improve the fault-tolerant performance of directed double-loop networks G(N;h)

the distribution about equal nodes for fault-tolerant nodes of directed double-loop networks G(N;h)was studied

and presented a way to find the fault-tolerant routing algorithm of double-loop networks G(N;h).That is

when the shortest path fails between any two nodes of the double-loop networks

how to find the other one.The time complexity of the algorithm is O(d).