Abstract: A method, in a relay-based wireless communication system, for performing downlink ARQ process, is proposed according to the invention. The method comprises: the BS sends first data to the RS, the first data multiplexing second data for one or more terminal equipments; if the transmission of the first data fails, unsolicited ARQ process to the RS is triggered by the BS, so as to perform the retransmission of the first data; the RS demultiplexs the first data transmitted from the BS to generate the second data, and sends the demultiplexed second data to the terminal equipment; if the transmission of the second data fails, the unsolicited ARQ process to the terminal equipment is triggered by the RS, so as to perform the retransmission for the second data; and the terminal equipment receives the second data and triggers a passive ARQ process for the reception of the second data.