A base station, a terminal, a system and methods for performing data transmission in a Time Division Duplex (TDD) system are disclosed. One of the methods includes: the base station sending an uplink scheduling grant signaling to the terminal on a carrier m, and after receiving uplink data sent by the terminal through a Physical Uplink Shared Channel (PUSCH) on a carrier n, the base station sending an ACK/NACK feedback signaling corresponding to the PUSCH to the terminal on the carrier m; wherein, m≠n; a timing relationship between a subframe by which the base station sends the uplink scheduling grant signaling and/or the ACK/NACK feedback signaling and a subframe where the PUSCH is located is identical with a Hybrid Automatic Repeat Request (HARQ) timing relationship corresponding to an uplink/downlink configuration of the carrier m or the carrier n.