The present invention discloses a method and a system for implementing alternative routes in optical transmission network of WSON. By using the method and the system the following alternative routes implementing process is realized: computing the alternative routes of each subsegment independently based on a constraining condition distributed by a managing plane, and combining the computed alternative routes of each subsegment to form complete alternative routes. The present method and system for implementing alternative routes is capable of obtaining more alternative routes than those of prior art, and takes full advantage of network resource topology.