As the instantaneous Channel State Information (CSI) of source to relay and relay to destination affects the overall Bit Error Rate (BER) of the cooperative communication system, a relay selection scheme which evaluated the two-stage channel coefficients was proposed. Firstly, the channel coefficients of source-relay channel and the channel coefficients of relay-destination channel were compared according to the CSI of each candidate relay, and the worse one was found out. Moreover, a node set containing the approximate optimal relays was obtained by sorting the candidate relays based on their worse channel coefficients. Finally, the relay with the highest summation of the two-stage channel coefficients in the set was selected as the one which participated in the cooperative transmission. The simulation results reveal that the Signal-to-Noise Ratio (SNR) of the proposed relay selection scheme respectively decreases by 0.4 dB and 0.2 dB compared with the best worse channel selection scheme and the delay selection scheme based on the nearest neighbor relation, when the number of candidate relay nodes is 100 and 5, and the BER decreases to 10^-4 and 10^-5. In general, the proposed scheme can expend the information transmission range and improve the reliability in the wireless relay network.