Implementations of the present disclosure relate to a method for transmitting data and a terminal device. The method includes: if there is an untransmitted first MAC PDU in a target HARQ process, sending a third MAC PDU to a physical layer at an MAC layer, wherein, a first resource corresponding to the first MAC PDU overlaps with a second resource corresponding to a second MAC PDU, the third MAC PDU includes data in the first MAC PDU, and the physical layer is used for transmitting the third MAC PDU through a third resource.