A data transmission method, comprising: receiving, by a terminal device, a first indication sent by a network device; receiving, by the terminal device, downlink data based on the first indication, and generating feedback information of the downlink data; receiving, by the terminal device, a second indication sent by the network device after obtaining an unlicensed channel, wherein the second indication is used to indicate a start location of an uplink time unit; determining, by the terminal device based on the first indication and the second indication, a time-frequency resource location for sending the feedback information; and sending, by the terminal device, the feedback information at the determined time-frequency resource location; wherein the first indication comprises a valid time range, wherein the first indication is used to instruct the terminal device to receive, within the valid time range, the second indication sent by the network device, and the receiving, by the terminal device, a second indication sent by the network device comprises: receiving, by the terminal device within the valid time range, the second indication sent by the network device; wherein before the sending, by the terminal device, the feedback information at the time-frequency resource location, the method further comprises: performing, by the terminal device, listen before talk, LBT, channel detection, and detecting that a channel is a clear channel; and wherein the method further comprises: when a discontinuous reception, DRX, mechanism is configured for the terminal device by the network device, if the second indication is received within the valid time range, stopping monitoring a downlink physical channel from a reception moment where the second indication is received to expiration of the valid time range. receiving, by a terminal device, a first indication sent by a network device; receiving, by the terminal device, downlink data based on the first indication, and generating feedback information of the downlink data; receiving, by the terminal device, a second indication sent by the network device after obtaining an unlicensed channel, wherein the second indication is used to indicate a start location of an uplink time unit; determining, by the terminal device based on the first indication and the second indication, a time-frequency resource location for sending the feedback information; and sending, by the terminal device, the feedback information at the determined time-frequency resource location; wherein the first indication comprises a valid time range, wherein the first indication is used to instruct the terminal device to receive, within the valid time range, the second indication sent by the network device, and the receiving, by the terminal device, a second indication sent by the network device comprises: receiving, by the terminal device within the valid time range, the second indication sent by the network device; wherein before the sending, by the terminal device, the feedback information at the time-frequency resource location, the method further comprises: performing, by the terminal device, listen before talk, LBT, channel detection, and detecting that a channel is a clear channel; and wherein the method further comprises: when a discontinuous reception, DRX, mechanism is configured for the terminal device by the network device, if the second indication is received within the valid time range, stopping monitoring a downlink physical channel from a reception moment where the second indication is received to expiration of the valid time range.