A data transmission method, comprising: sending, by a network device, first data to a terminal in a first subframe through a first channel, wherein the first channel is a channel occupied in a channel system by a service between the network device and the terminal; performing, by the network device, channel listening on a channel that is not occupied in the channel system by the service; and when there is a second channel in an idle state, sending, by the network device, second data of the service to the terminal in a second subframe through the first channel and the second channel, wherein the second subframe is after the first subframe, wherein the service comprises the first data and the second data, and a data frame of the service comprises the first subframe and the second subframe; characterized in that the first subframe is a downlink subframe; and the performing, by the network device, channel listening on a channel that is not occupied in the channel system by the service comprises: performing, by the network device in a time period corresponding to N downlink symbols in the first subframe, listening on the channel that is not occupied in the channel system by the service, wherein N is a positive integer, and the N downlink symbols do not carry data; and wherein the data frame of the service further comprises a third subframe and a fourth subframe, the third subframe is an uplink subframe, the fourth subframe is a downlink subframe, the third subframe is adjacent to the fourth subframe, the third subframe is before the fourth subframe, the third subframe is after the second subframe, and the service further comprises third data; and the method further comprises: performing, by the network device in a time period corresponding to the third subframe, channel listening on a channel that is not occupied in the channel system by the service; and when there is a third channel in the idle state, sending, by the network device, the third data to the terminal in the fourth subframe through the first channel, the second channel, and the third channel. sending, by a network device, first data to a terminal in a first subframe through a first channel, wherein the first channel is a channel occupied in a channel system by a service between the network device and the terminal; performing, by the network device, channel listening on a channel that is not occupied in the channel system by the service; and when there is a second channel in an idle state, sending, by the network device, second data of the service to the terminal in a second subframe through the first channel and the second channel, wherein the second subframe is after the first subframe, wherein the service comprises the first data and the second data, and a data frame of the service comprises the first subframe and the second subframe; characterized in that the first subframe is a downlink subframe; and the performing, by the network device, channel listening on a channel that is not occupied in the channel system by the service comprises: performing, by the network device in a time period corresponding to N downlink symbols in the first subframe, listening on the channel that is not occupied in the channel system by the service, wherein N is a positive integer, and the N downlink symbols do not carry data; and wherein the data frame of the service further comprises a third subframe and a fourth subframe, the third subframe is an uplink subframe, the fourth subframe is a downlink subframe, the third subframe is adjacent to the fourth subframe, the third subframe is before the fourth subframe, the third subframe is after the second subframe, and the service further comprises third data; and the method further comprises: performing, by the network device in a time period corresponding to the third subframe, channel listening on a channel that is not occupied in the channel system by the service; and when there is a third channel in the idle state, sending, by the network device, the third data to the terminal in the fourth subframe through the first channel, the second channel, and the third channel. performing, by the network device in a time period corresponding to N downlink symbols in the first subframe, listening on the channel that is not occupied in the channel system by the service, wherein N is a positive integer, and the N downlink symbols do not carry data; and wherein the data frame of the service further comprises a third subframe and a fourth subframe, the third subframe is an uplink subframe, the fourth subframe is a downlink subframe, the third subframe is adjacent to the fourth subframe, the third subframe is before the fourth subframe, the third subframe is after the second subframe, and the service further comprises third data; and the method further comprises: performing, by the network device in a time period corresponding to the third subframe, channel listening on a channel that is not occupied in the channel system by the service; and when there is a third channel in the idle state, sending, by the network device, the third data to the terminal in the fourth subframe through the first channel, the second channel, and the third channel. performing, by the network device in a time period corresponding to the third subframe, channel listening on a channel that is not occupied in the channel system by the service; and when there is a third channel in the idle state, sending, by the network device, the third data to the terminal in the fourth subframe through the first channel, the second channel, and the third channel.