The present invention relates to a wireless communication system and, more specifically, to a method and an apparatus for reporting channel state information (CSI). According to one embodiment of the present invention, the method by which a terminal of the wireless communication system reports the CSI comprises: a step of receiving a reference signal from a base station; and a step of reporting the CSI generated through the reference signal to the base station. The CSI can include information for indicating a first pre-coding matrix for a first domain of a two-dimensional antenna structure and a second pre-coding matrix for a second domain of the two-dimensional antenna structure. The first pre-coding matrix can be determined on the basis of a coefficient wherein an angle the first domain is determined according to an angle in the second domain.