Embodiments of the present disclosure related to a method for configuring a transmission resource, a related device, and a communication system. The method for configuring a transmission resource includes: notifying, by an access device, a user equipment of an uplink-downlink configuration change period, where the uplink-downlink configuration change period is less than a system message change period; and sending, by the access device, a first message to the user equipment, where the first message carries an uplink-downlink configuration indication corresponding to the uplink-downlink configuration change period, so that the user equipment updates, according to the uplink-downlink configuration indication, an uplink-downlink configuration used by the user equipment. The solutions according to the embodiments of the present disclosure help to improve flexibility for configuring a transmission resource and a utilization rate of a frequency spectrum resource.