The present invention relates to a wireless communication system and, more particularly, to a method and device for compressing and feeding back channel information in a wireless communication system supporting a multi-input multi-output (MIMO) scheme. A method for feeding back channel information by a terminal in a wireless communication system supporting a MINO scheme, according to one embodiment of the present invention, can comprise the steps of: calculating a channel matrix on the basis of a reference signal received from a base station; calculating a first valid channel vector by using a reception weight vector and the channel matrix; and calculating a second valid channel vector by setting a coefficient corresponding to each basis vector included in a basis matrix as 0 if the coefficient is equal to or less than a threshold when the first valid channel vector is factored by the basis matrix.