In an aspect of the present invention, a method for transmitting channel state information (CSI) of terminal in a wireless communication system may include: receiving a CSI-reference signal (RS); generating a first matrix for a channel based on the CSI-RS; generating a second matrix having a lower dimension than the first matrix by calculating the first matrix and an orthogonal beam matrix having a lower dimension than the first matrix; and transmitting to a base station information on the second matrix and/or the orthogonal beam matrix as the CSI, in which the orthogonal beam matrix may be a matrix including a plurality of orthogonal beams orthogonal to each other as elements.