A data transmission method, including: determining, according to a maximum power value detected by performing a CCA on a primary channel in one or more processing time periods, a power value interval to which the maximum power value detected by performing the CCA belongs, where the determined power value interval is one of one or more power value intervals that do not overlap each other; obtaining a transmit power spectral density according to the determined power value interval, where there is a one-to-one correspondence between the one or more power value intervals and one or more transmit power spectral densities; and when a TXOP is obtained, performing data transmission on a transmission channel by using a power spectral density that is not greater than the transmit power spectral density.