Embodiments of the present invention provide a protection switching method, network node, and system, where a communication method includes: when a first transport entity changes from a standby state to an active state, determining that in a second protected domain, there is only a protection transport entity that is connected to the first boundary node; switching a service to a first protection transport entity; and sending a first automatic protection switching APS message that carries a request of triggering inter-domain protection switching. By using the protection switching method, network node, and system that are provided by the embodiments of the present invention, end-to-end protection switching may be implemented, which enhances robustness of a protection network.