A protection method in the packet transport network is provided by the embodiment of the invention. A protection path for the service data flow bearing on the shared protection ring is set up in the method, wherein the protection path includes a loopback protection path and a source routing protection path. Firstly, a first service data flow is sent through the loopback protection path. Then a service data flow node stops sending a second service data flow following the first service data flow to the loopback protection path, and caches the second service data flow. When the first service data flow completely passes the service data flow node again, the cached second service data flow is switched from the loopback protection path to the source routing protection path. A relevant system and device are also provided by the embodiment of the invention. The invention can solve the disordering problem generated when the combination protection scheme of the loopback way and the source routing way is applied in the packet transport network.