An adaptive transmit power allocation (TPA) scheme to minimize bit error rate (BER) is investigated in a vertical bell labs layered space-time (V-BLAST) system with channel correlation and estimation error. The closed expression for average BER can be derived according to the instantaneous signal-to-interference-plus-noise ratio (SINR) of each sub-stream by system modeling and performance analysis. At the transmitter, with the total TPA constraint condition, TPA matrix is calculated through the Lagrange multiplier method. Numerical results demonstrate that the correlation structure and channel estimation error have a profound effect on the performance of V-BLAST system. The proposed TPA scheme can improve the BER performance effectively and be practical for the actual communication system.