A network management method, device, and system used for network management and pertains to the communications field, where the method includes detecting bandwidth required by a first data flow, determining whether the bandwidth required by the first data flow is greater than a preset bandwidth value when the bandwidth required by the first data flow becomes higher, and allocating bandwidth to the first data flow when the bandwidth required by the first data flow is greater than the preset bandwidth value. Hence, a problem that a controller has relatively low efficiency when performing network management is resolved, thereby improving efficiency of performing network management by the controller.