Double-loop is a very popular structure in loop network topology. Areconfigurable bi-directional double-loop structure is recentlydeveloped. It has a new structure which is different from any existingdouble-loop structure and no previous methods can be used to evaluateits fault tolerance which is demanded for all fresh ideas. This paperprovides an easy approach to offset this deficiency. A network issegmented first based on its block connection and then analyzed in arecursive way. The calculation using this method requires linear timeand very small memory capacity. This method can be used in analyzing thefault tolerance of other topologically segmental loop networks.