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 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 .