A communication method includes receiving, by a terminal device, on an unlicensed frequency band, downlink control information sent by a network device, where the downlink control information is within a first time unit in a candidate time unit set of a plurality of candidate time unit sets, where the candidate time unit set is at least one of a plurality of consecutive time units, and wherein the candidate time unit sets are at equal intervals in the plurality of consecutive time units. The method further includes determining, by the terminal device according to a time at which the downlink control information is sent, a time window for sending uplink information, and sending, by the terminal device, the uplink information within the time window, where a start moment T1 of the time window is within the first time unit or a second time unit immediately after the first time unit.