Embodiments of the present invention provide a data transmission method and apparatus. The method includes: determining a contention transmission unit CTU to be used by to-be-sent uplink data, where the CTU is a transmission resource including at least a time domain resource, a frequency domain resource, and a code domain resource; encoding the to-be-sent uplink data by using N different code element groups in the code domain resource corresponding to the determined CTU, to obtain N groups of encoded data, where N is a positive integer greater than or equal to 2; and sending the N groups of encoded data by using the time domain and frequency domain resources that are corresponding to the determined CTU. According to the embodiments of the present invention, data reception reliability at a receive end can be improved.