A terminal device receives first scheduling information from an access network device, where the first scheduling information is used to schedule the terminal device to transmit a first transport block by using an unlicensed carrier; performs rate matching on the first transport block, to obtain uplink data; detects the unlicensed carrier, and determines a start time domain symbol, used to send the uplink data, in at least two time domain symbols included in a first subframe, where the at least two time domain symbols include a first time domain symbol and a second time domain symbol, the second time domain symbol is later than the first time domain symbol, and the start time domain symbol is the first time domain symbol or the second time domain symbol; and sends the uplink data to the access network device from the start time domain symbol.