Disclosed are a method, device, system for detecting a data link, controller, and gateway. The method comprises: an SDN controller sends a GTP request message to a first UGW, and instructs the first UGW to send the GTP request message to another GTP endpoint in a GTP user plane signaling format; the SDN controller receives a GTP response message from the first UGW, and detects a data link between the first UGW and the another GTP endpoint according to the GTP response message, the GTP response message being corresponding to the GTP request message. The disclosure solves the problem in the prior art that logic of a user plane and logic of a control plane are unclear during detection of a data link between GTP endpoints, thereby improving the clarity of the logic of the user plane and the clarity of the logic of the control plane.