The present invention relates to a wireless communication system, and provides a method and an apparatus for transmitting a downlink reference signal in the wireless communication system. The method for enabling a base station to transmit the reference signal to a terminal using layers of 8 or less in accordance with one embodiment of the present invention comprises the steps of: transmitting data for the layers of 8 or less through a data domain of a downlink sub frame; and transmitting a reference signal for the layers of 8 or less on a fixed OFDM symbol of the downlink sub frame, wherein the reference signal is a DRS (Dedicated Reference Signal) which demodulates the data for the layers of 8 or less, and the reference signal for the layers of 8 or less is separated into 1st and 2nd groups, and reference signals of the 1st and 2nd groups can be multiplexed in a CDM (Code Division Multiplexing) method on one resource element, respectively.