A data transmission method and an apparatus are provided. The method includes: determining, by a base station, a time-domain interval of available time-frequency resources in an unlicensed spectrum, where the available time-frequency resources are continuous time-frequency resources in a time domain; sending, by the base station, a preamble signal in a first subframe in the interval, where the first subframe is an initial subframe in the interval; and sending, by the base station, downlink control information and data after sending the preamble signal, where the data is in the first subframe, the downlink control information includes scheduling indication information, and the scheduling indication information is used to indicate a frequency-domain location of the data. According to the present invention, spectrum utilization can be improved.