Embodiments of this application provide a data transmission method and device, so as to increase an uplink/downlink data transmission throughput. The method includes: splitting a to-be-transmitted transport block into N code blocks with incompletely equal sizes, where N is an integer greater than or equal to 2; performing error correction coding on the N code blocks to obtain N encoded bit blocks; and non-orthogonally transmitting the N encoded bit blocks by using resources that are the same in at least one dimension of a time domain, a frequency domain, a space domain, and a code domain.