A method is provided for transmitting, by a user equipment (UE), a demodulation reference signal (DMRS) in a wireless communication system. A first DMRS sequence, which is associated with a first layer, and a second DMRS sequence, which is associated with a second layer, are transmitted to a base station. A first orthogonal cover code (OCC) is applied to the first and second DMRS sequences. A third DMRS sequence, which is associated with a third layer, and a fourth DMRS sequence, which is associated with a fourth layer, are transmitted to the base station. A second OCC is applied to the third and fourth DMRS sequences.