A protection method in a packet transport network is provided. A protection path is established for a service data flow borne on a shared protection ring in the method, where the protection path includes a wrapping protection path and a steering protection path. Firstly, a first service data flow is sent through the wrapping protection path. Then, a service data flow node stops sending a second service data flow subsequent to the first service data flow to the wrapping protection path, and buffers the second service data flow. When the first service data flow completely passes by the service data flow node again, the buffered second service data flow is switched from the wrapping protection path to the steering protection path.