The method includes following procedures: when information of network topology structure of nodes of MPLS ring net is needed to update, corresponding nodes send discovered message of topology automatically through built label switch path (LSP); the message carries information of topology structure of change happened nodes passed in ring net; when the discovered message of topology returns back, information of network topology structure saves in the node is updated based on content carried in the message. MPLS ring net is built in MPLS layer. Ling net topology structure of automatic discoveringlogic is not dependent on network topology in physical layer so as to quicken speed for automatic discovering topology structure of ring net.