This application provides a data transmission method, a terminal device, and a network device. The method includes: determining, by a terminal device, reference information indicating a threshold associated with a quantity of resource elements (REs) configured for all or a portion of channel state information (CSI) on an uplink channel; and sending, by the terminal device, the all or the portion of the CSI based on a comparison result of the reference information and a status parameter, wherein the status parameter indicates a quantity of REs occupied by the CSI on the uplink channel.