A data transmission method in a time division duplex wireless data transmission system, comprising: generating, by a first transmission device, an idle frame and a service frame; sending, by the first transmission device, the service frame to a second transmission device; sending, by the first transmission device, the idle frame to the second transmission device after each time the first transmission device sends a preset quantity of service frames to the second transmission device; receiving, by the second transmission device, a service frame sent by the first transmission device, and receiving the idle frame that is sent by the first transmission device after each time the first transmission device sends a preset quantity of service frames; performing, by the second transmission device in a timeslot corresponding to the idle frame, interference detection on a to-be-detected frequency band corresponding to the idle frame in an available spectrum, wherein the available spectrum is divided into to-be-detected frequency bands according to a preset sequence and each to-be-detected frequency band is associated with a different idle frame, obtaining an interference detection result of the to-be-detected frequency band, and updating the interference detection result of the to-be-detected frequency band in interference statistics of the available spectrum; and switching, by the second transmission device according to the interference statistics of the available spectrum when interference to a current operating frequency band is greater than a preset threshold, the operating frequency band to a frequency band that meets a preset condition. generating, by a first transmission device, an idle frame and a service frame; sending, by the first transmission device, the service frame to a second transmission device; sending, by the first transmission device, the idle frame to the second transmission device after each time the first transmission device sends a preset quantity of service frames to the second transmission device; receiving, by the second transmission device, a service frame sent by the first transmission device, and receiving the idle frame that is sent by the first transmission device after each time the first transmission device sends a preset quantity of service frames; performing, by the second transmission device in a timeslot corresponding to the idle frame, interference detection on a to-be-detected frequency band corresponding to the idle frame in an available spectrum, wherein the available spectrum is divided into to-be-detected frequency bands according to a preset sequence and each to-be-detected frequency band is associated with a different idle frame, obtaining an interference detection result of the to-be-detected frequency band, and updating the interference detection result of the to-be-detected frequency band in interference statistics of the available spectrum; and switching, by the second transmission device according to the interference statistics of the available spectrum when interference to a current operating frequency band is greater than a preset threshold, the operating frequency band to a frequency band that meets a preset condition.