Embodiments of the present application disclose a method for transmitting data, a terminal device, and a network device, where the method includes: receiving, by a terminal device, first indication information sent by a network device, where the first indication information indicates that data is capable of being transmitted on a semi-persistent scheduling resource within a first bandwidth part BWP of at least one BWP and where the first BWP is in an active state; determining, by the terminal device, the semi-persistent scheduling resource within the first BWP according to the first indication information; and performing, by the terminal device, data transmission on the semi-persistent scheduling resource within the first BWP with the network device. The method, the terminal device and the network device in the embodiments of the present application are beneficial to improving an accuracy of data transmission.