A control device, a system, and a transmission channel adjustment method in software-defined networking (SDN) where, a connection status of a control channel is acquired, it is determined, according to a preset threshold, whether a standby channel is suitable to continue serving as a standby channel. The standby channel is adjusted when the standby channel is congested to a specific extent and another uncongested channel is set as the standby channel, and the standby channel is switched to an active channel when the active channel is congested such that real-time channel adjustment is ensured, effective transmission of control information is ensured, and control reliability of a control device in SDN is improved.