A method for detecting degraded signal defects, characterized by comprising: a packet transport network trail enabling a degraded signal defects detection and configuring a degradation threshold DEGTHR_M, a degradation detection period DEG_ENTRY_M and an exit period DEG_EXIT_M; each node that the packet transport network trail passes enabling a server layer degraded signal defects detection and configuring a node degradation threshold DEGTHR_N, a node degradation detection period DEG_ENTRY_N, a node exit period DEG_EXIT_N, a threshold of the total number of messages received by nodes RF_MIN and a threshold of forward error indication, FEI, messages transmitted by nodes FEITHR_N for said nodes whose server layer degraded signal defects detection is enabled, calculating a packet loss ratio on a receiving port, and performing following two judgments: when the packet loss ratio is greater than the DEGTHR_N and a duration reaches the DEG_ENTRY_N, the server layer degraded signal defect occurring, and when the packet loss ratio is less than the DEGTHR_N and the duration reaches the DEG_EXIT_N, the server layer degraded signal defect disappearing; when the packet loss ratio is greater than the FEITHR_N, sending downstream the FEI messages to the packet transport network trail that passes the server layer, and when the packet loss ratio is less than the FEITHR_N, stopping sending the FEI messages; wherein the FEI message includes a state of the server layer degraded signal defect, ID of the node that sends the FEI messages and the packet loss ratio of the server layer; the packet transport network trail detecting whether the degraded signal defect occurs in last node or not according to the FEI message information received from upstream nodes. a packet transport network trail enabling a degraded signal defects detection and configuring a degradation threshold DEGTHR_M, a degradation detection period DEG_ENTRY_M and an exit period DEG_EXIT_M; each node that the packet transport network trail passes enabling a server layer degraded signal defects detection and configuring a node degradation threshold DEGTHR_N, a node degradation detection period DEG_ENTRY_N, a node exit period DEG_EXIT_N, a threshold of the total number of messages received by nodes RF_MIN and a threshold of forward error indication, FEI, messages transmitted by nodes FEITHR_N for said nodes whose server layer degraded signal defects detection is enabled, calculating a packet loss ratio on a receiving port, and performing following two judgments: when the packet loss ratio is greater than the DEGTHR_N and a duration reaches the DEG_ENTRY_N, the server layer degraded signal defect occurring, and when the packet loss ratio is less than the DEGTHR_N and the duration reaches the DEG_EXIT_N, the server layer degraded signal defect disappearing; when the packet loss ratio is greater than the FEITHR_N, sending downstream the FEI messages to the packet transport network trail that passes the server layer, and when the packet loss ratio is less than the FEITHR_N, stopping sending the FEI messages; wherein the FEI message includes a state of the server layer degraded signal defect, ID of the node that sends the FEI messages and the packet loss ratio of the server layer; when the packet loss ratio is greater than the DEGTHR_N and a duration reaches the DEG_ENTRY_N, the server layer degraded signal defect occurring, and when the packet loss ratio is less than the DEGTHR_N and the duration reaches the DEG_EXIT_N, the server layer degraded signal defect disappearing; when the packet loss ratio is greater than the FEITHR_N, sending downstream the FEI messages to the packet transport network trail that passes the server layer, and when the packet loss ratio is less than the FEITHR_N, stopping sending the FEI messages; wherein the FEI message includes a state of the server layer degraded signal defect, ID of the node that sends the FEI messages and the packet loss ratio of the server layer; the packet transport network trail detecting whether the degraded signal defect occurs in last node or not according to the FEI message information received from upstream nodes.