1. An apparatus for transmitting in a multi-user multi-antenna system, the apparatus comprising: a precoder configured to orthogonalize a channel by removing a channel element of a corresponding terminal with respect to multiple terminals, to determine an effective channel of each terminal by decomposing the orthogonalized channel using Singular Value Decomposition (SVD), to determine a precoding matrix using the effective channel, and to map data streams of the multiple terminals to a plurality of transmit antennas using the precoding matrix, wherein, iteratively by as many times as the number of the multiple users, the precoder decomposes each channel orthogonalization matrix of the multiple terminals using the SVD, selects a terminal of a maximum singular value among the multiple terminals, and removes the channel element of the selected terminal; and the plurality of the transmit antennas configured to transmit the data streams of the multiple terminals.