Abstract: An in-situ flow detection method and a related device are disclosed pertaining to the field of communication technologies. The method includes, when a tunnel type of an uplink tunnel of a first node is inconsistent with a tunnel type of a downlink tunnel of the first node, the first node generates a second traffic detection header based on a first traffic detection header. Therefore, the first node can continue to send, to a next hop without using an IFIT indication delivered by a control node, a packet that carries a traffic detection header, so that in-situ flow detection across tunnels of different types is implemented.