A data transmission method and a communications device resolve an existing problem that use of an unlicensed spectrum is interfered with between LTE devices when a padding is sent. The method includes: performing, by a communications device, CCA on an unlicensed spectrum; and when determining that the unlicensed spectrum is in an idle state, sending, by the communications device on a preset band resource in the unlicensed spectrum, a signal indicating that the communications device uses the unlicensed spectrum, where the preset band resource is a partial band resource in the unlicensed spectrum. Mutual interference between communications devices when the unlicensed spectrum is used is eliminated.