A method for automatically implementing Tandem Concatenation Monitoring (TCM), includes: requesting a network management system for a required number of TCM levels; assigning an available TCM level to a pair of network nodes in a sub-network; performing TCM processing, mapping TCM use information into a corresponding overhead, transferring the TCM use information together with TCM overhead information downstream, and reporting TCM information to the network management system; and extracting TCM monitored information, determining transmission quality of each sub-network of a set of sub-networks, and locating a network failure. The invention also presents a device for automatically implementing TCM, including a controller, a TCM generator and a TCM terminator which cooperate with each other to automatically implementing a TCM function. The invention addresses the poor flexibility and complexity due to a static configuration by the network management system, and thus improves the flexibility of the TCM processing.