A method for determining uplink transmission power in time division duplex system is disclosed: a base station determines the current distribution manner of uplink and downlink sub-frames, acquires the frame correspondence information that corresponds to the distribution manner of said uplink and downlink sub-frames, selects, based on said frame correspondence information, downlink sub-frames to transmit to a terminal the power control (TPC) commands that correspond to the uplink sub-frames. Before using the uplink sub-frames to transmit data, the terminal determines the current distribution manner of uplink and downlink sub-frames, acquires the frame correspondence information that corresponds to the distribution manner of said uplink and downlink sub-frames, determines, based on the frame correspondence information, the downlink sub-frames that are used for transmitting the TPC commands; acquires the TPC commands received by the downlink sub-frames, and determines the data transmission power of the uplink sub-frames based on said TPC commands. The present invention also discloses a time division duplex data transmission system and an apparatus therefor. With the present invention, a time division duplex system can transmit and receive TPC commands based on the frame correspondence information, thereby enabling correct and effective uplink power control performance.