A data transmission method and an apparatus relate to the communications field and are applied to data transmission to effectively reduce a collision reoccurrence probability after a device in a licensed-assisted access using Long Term Evolution (LAA-LTE) system preempts an unlicensed spectrum and collides with another device. A first device adjusts a detection moment or a quantity of detection times of clear channel assessment (CCA) of a channel in an unlicensed spectrum after the first device determines that the first device collides with another device when occupying the channel in the unlicensed spectrum to transmit data, and the first device occupies, according to an adjusted detection moment or an adjusted quantity of detection times of CCA of the channel in the unlicensed spectrum, the channel in the unlicensed spectrum to transmit data.