A data transmission method, a terminal device and a network device are provided. The method comprises: a terminal device receives configuration information sent by a network device, wherein the configuration information is used to configure one or more slot format indictors (SFIs) corresponding to one or more 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 performs data transmission according to the target SFI.