Provided is a method for transmitting a reference signal (RS) in a downlink multi-input multi-output (MIMO) system which supports a first user equipment (UE) for supporting N transmission antennas from among a total of M transmitting antennas and a second UE for supporting M transmitting antennas (wherein, M>N). The method comprises the steps of: generating a subframe for simultaneously supporting the first UE and the second UE at a base station; transmitting the subframe; and mapping a common reference signal (CRS) for antenna port 0 to antenna port N−1, mapping a CRS for antenna port N to antenna port M−1, and controlling a power level of a CRS for antenna port 0 to antenna port N−1 and a power level of CRS for antenna port N to antenna port M−1, independently from one another, at the subframe.