Embodiments of the present application provide a data transmission method, a terminal device and a network device, by which SFIs can be configured in presence of multiple BWPs. The method comprises: a terminal device receives configuration information sent by a network device, the configuration information being used to respectively configure corresponding slot format indictors (SFIs) for multiple bandwidth parts (BWPs) configured for the terminal device; the terminal device determines a currently-used target SFI according to the configuration information; and the terminal device transmits data according to the target SFI.