Abstract: In order to reduce the complexity of transmit antenna selection in Multi-Input and Multi- Output(MIMO) systems using Linear Dispersion Codes(LDC), an approximate capacity expression considering the average effect of LDC matrix is derived making use of the characterization of unitary-based parameterization of Linear Transformation Matrix for LDC. Transmit antenna selection algorithms based on approximate capacity can lower the complexity efficiently, because the approximate capacity expression does not involve the operations about higher-order equivalent channel matrix extended in time. From the approximate capacity expression, transmit antenna selection algorithms based on maximum approximate capacity and based on matrix elimination are proposed in this paper separately, and meanwhile approximate capacity expression offers theory support for direct use of some transmit antenna selection algorithms proposed in vertical-bell laboratory layered space-time (V-BLAST) systems. Simulation results suggest that the proposed algorithms can approach the performance of optimal antenna selection algorithm with lower complexity. Compared to the norm and correction-based algorithm proposed in V-BLAST systems, the algorithm based on matrix elimination can get better diversity gain, and outperform the former on Bit Error Rate(BER) performance.