Embodiments of this application provide a method for obtaining a target transmission route, a related device, and a system. The method is applied to a flexible Ethernet FlexE networking network and includes: receiving a first message that is sent by a second node for requesting to query for a transmission route of a first FlexE client; and sending a second message to the second node, where a route information entry in the second message includes route information of the FlexE client on each node. Ingress information and egress information that are of a FlexE client on a route node are recorded as a transmission route of each hop. A segment-to-segment transmission route in the FlexE network can be dynamically found in real time, a planned and deployed transmission route is compared with an actually found route, to evaluate a network running status.