Embodiments of the present invention provide a method, device, and system for scheduling a data flow, which are used to improve the processing efficiency. A network side device marks a priority of a subsequent uplink and/or downlink data flow of a UE corresponding to a downlink data packet in the downlink data packet, and enables a downstream node to schedule an access network resource or air interface resource according to the priority. Therefore, a bearer does not need to be modified during the process of distinguishing different service flows and performing differentiation scheduling on different service flows, thereby reducing the workload and improving the processing efficiency.