A method for transmitting a demodulation reference signal over a backhaul link in a Long Term Evolution-Advanced, LTE-A, system, the method comprising selecting, by an eNodeB in a resource zone occupied by a Relay-Physical Downlink Shared Channel, R-PDSCH, over the backhaul link, preconfigured resource units for transmission of a demodulation reference signal of the R-PDSCH; and transmitting, by the eNodeB, the demodulation reference signal to a Relay Node, RN, subordinated to the eNodeB in the selected resource units; wherein the preconfigured resource units for transmission of the demodulation reference signal of the R-PDSCH are configured as follows by the eNodeB: determining the resource zone occupied by the R-PDSCH; selecting resource units in the resource zone, which are neither occupied by a common reference signal nor located at the last OFDM symbol of the resource zone; and configuring the selected resource units as the resource units for transmission of the demodulation reference signal of the R-PDSCH; characterized in that, in the case that the Code Division Multiplexing in frequency direction, CDM-F, mode is adopted for the demodulation reference signal, selecting the resource units in the resource zone, which are neither occupied by a common reference signal nor located at the last OFDM symbol of the resource zone comprises: searching the resource zone for resource units in an Long Term Evolution, LTE, system for transmission of the demodulation reference signal; and selecting the located resource units as the resource units in the resource zone, which are neither occupied by a common reference signal nor located at the last OFDM symbol of the resource zone; wherein the resource units for transmission of the demodulation reference signal of the R-PDSCH comprises: resource units consisting of the third OFDM symbols in a second timeslot of a sub-frame where the resource zone is located; in the case that the Code Division Multiplexing in time direction, CDM-T, mode is adopted for the demodulation reference signal and the number of OFDM symbols covered by a resource zone occupied by a Relay-Physical Downlink Control Channel, R-PDCCH, over the backhaul link is less than or equal to 2, selecting the resource units in the resource zone, which are neither occupied by a common reference signal nor located at the last OFDM symbol of the resource zone comprises: searching the resource zone occupied by the R-PDSCH for resource units in an LTE system for transmission of the demodulation reference signal; translating the located resource units at the last two OFDM symbols of the resource zone occupied by the R-PDSCH onto resource units in the resource zone, which are not occupied by a common reference signal; and selecting the located resource units at the first two OFDM symbols of the resource zone occupied by the R-PDSCH and the translated resource units as the resource units in the resource zone, which are neither occupied by a common reference signal nor located at the last OFDM symbol of the resource zone; in the case that the CDM-T mode is adopted for the demodulation reference signal and the number of OFDM symbols covered by a resource zone occupied by a Relay-Physical Downlink Control Channel, R-PDCCH, over the backhaul link is larger than 2, selecting the resource units in the resource zone, which are neither occupied by a common reference signal nor located at the last OFDM symbol of the resource zone comprises: searching the resource zone occupied by the R-PDSCH for resource units in an LTE system for transmission of the demodulation reference signal; translating the located resource units at the last two OFDM symbols of the resource zone occupied by the R-PDSCH onto resource units in the resource zone, which are not occupied by a common reference signal; and selecting the translated resource units as the resource units in the resource zone, which are neither occupied by a common reference signal nor located at the last OFDM symbol of the resource zone.