A method and device for transmitting a reference signal in a wireless communication system is provided. A base station maps each demodulation reference signal (DMRS) of each of a plurality of layers into a first resource element (RE) set and a second RE set including four REs over four orthogonal frequency division multiplexing (OFDM) symbols within a subframe, allocates first orthogonal cover codes (OCCs) having a length of 4 to each DMRS mapped into the first RE set, allocates second OCCs having a length of 4 to each DMRS mapped into the second resource element set and transmits each DMRS mapped into the first RE set and the second RE set. The subframe includes two slots and each slot includes six OFDM symbols. The second OCC are formed by swapping positions of bits that constitute the first OCCs.