Disclosed are a data transmission method, a terminal device, and a network device. The method comprises: a terminal device receiving a system information block SIB1 broadcast by a network device, wherein the SIB1 comprises frequency point information of an uplink carrier; and the terminal device determining, according to the frequency point information of the uplink carrier, an uplink bandwidth part (BWP) associated with a downlink BWP for broadcasting the SIB1.