Abstract: In order to overcome the disadvantages that fault diagnosis and localization mechanism hasn't supported differentiated survivability strategy, can't be triggered by itself, and the control traffic has been vast in MPLS (multi-protocol label switching) networks, a service-related self fault diagnosis and localization mechanism is provided. The provided mechanism sets a path between source node and destination node which is irrelevant to the work path, and the set path and work path form a ring, then the service-related self fault diagnosis and localization mechanism can be triggered automatically and control packages are transformed along the ring when the QoS of service declined. Simulation results show that the provided mechanism can not only ascertain the fault type and location accurately, provides milliseconds level fault diagnosis and localization time, but it also uses less control packages.