A data transmission method and a device are provided. The data transmission method is applied to a terminal and includes: in the case that both a grant-free resource and a grant-based resource are available for the terminal, choosing, by the terminal, to transmit service data on the grant-free resource preferentially; or choosing, by the terminal, to transmit service data on the grant-based resource preferentially; or choosing dynamically, by the terminal, to transmit service data on the grant-free resource and/or the grant-based resource.