A method of transmitting a reference signal performed by a Relay Station (RS) in a wireless communication system comprises allocating a guard time in the front of a backhaul subframe or the end of the backhaul subframe, the backhaul subframe comprising a plurality of slots, each of the plurality of slots comprising a plurality of Orthogonal Frequency Division Multiplexing (OFDM) symbols, and the guard time being a time interval for switching between an access link and a backhaul link, and transmitting a Demodulation Reference Signal (DMRS) to a Base Station (BS) in an OFDM symbol of the backhaul subframe. The OFDM symbol for the DMRS is not over-lapped with the guard time.