A protection switching method, wherein the method comprises: detecting, by a first boundary node, a first transport entity that is connected to the first boundary node and in a first protected domain changes from a standby state to an active state; checking, by the first boundary node, that in a second protected domain, there is only a protection transport entity (2 and 3) that is connected to the first boundary node, and there is no working transport entity that is connected to the first boundary node, wherein the first boundary node is both a boundary node of the first protected domain and a boundary node of the second protected domain, determining, by the first boundary node, that in the second protected domain, there is only a protection transport entity that is connected to the first boundary node, and there is no working transport entity that is connected to the first boundary node, - switching, by the first boundary node, a service to a first protection transport entity (2 or 3), wherein the first protection transport entity is a transport entity that is connected to the first boundary node and in the second protected domain; and - sending, by the first boundary node on the first protection transport entity (2 or 3), a first automatic protection switching, APS, message that carries a request of triggering inter-domain protection switching to a second boundary node (D or E), wherein the second boundary node is a boundary node of both the second protected domain and a boundary node of a third protected domain. detecting, by a first boundary node, a first transport entity that is connected to the first boundary node and in a first protected domain changes from a standby state to an active state; checking, by the first boundary node, that in a second protected domain, there is only a protection transport entity (2 and 3) that is connected to the first boundary node, and there is no working transport entity that is connected to the first boundary node, wherein the first boundary node is both a boundary node of the first protected domain and a boundary node of the second protected domain, determining, by the first boundary node, that in the second protected domain, there is only a protection transport entity that is connected to the first boundary node, and there is no working transport entity that is connected to the first boundary node, - switching, by the first boundary node, a service to a first protection transport entity (2 or 3), wherein the first protection transport entity is a transport entity that is connected to the first boundary node and in the second protected domain; and - sending, by the first boundary node on the first protection transport entity (2 or 3), a first automatic protection switching, APS, message that carries a request of triggering inter-domain protection switching to a second boundary node (D or E), wherein the second boundary node is a boundary node of both the second protected domain and a boundary node of a third protected domain. - switching, by the first boundary node, a service to a first protection transport entity (2 or 3), wherein the first protection transport entity is a transport entity that is connected to the first boundary node and in the second protected domain; and - sending, by the first boundary node on the first protection transport entity (2 or 3), a first automatic protection switching, APS, message that carries a request of triggering inter-domain protection switching to a second boundary node (D or E), wherein the second boundary node is a boundary node of both the second protected domain and a boundary node of a third protected domain.