A method, an apparatus, and a system for locating a root cause of a network anomaly in the field of network technologies comprises, when a PFC deadlock occurs in a first egress port queue in a network device, the network device determines an abnormal data flow in the first egress port queue based on an access control list, where both an egress port and an ingress port of the abnormal data flow are uplink ports of the network device. The first egress port queue is any egress port queue in the network device. The network device sends anomaly information to a network management device, where the anomaly information includes an identifier of the abnormal data flow. The network management device transmits the identifier of the abnormal data flow to a display device for display by the display device.