Abstract: Those relays in deep fading are actually not helpful in the cooperation, and indeed they consume extra energy. Selecting one or multiple relays to forward signals based on a certain criteria can improve performance of a cooperative communication system. Therefore, relay selection in the cooperative communication system has gain increasing attention. In this paper, assume that a transmitter has no channel information and a receiver has complete information of channels in a wireless relay network with a single antenna in the transmitter, in the receiver, in the relays, respectively. Under an assumption that each relay has no any channel information, a single relay selection scheme which can maximize the signal-to-noise ratio and a multiple relay selection scheme based on relay ordering method are proposed in this paper. Furthermore, the pair-wise error probabilities of single relay selection and multiple relay selection when two relays are selected for relaying are calculated respectively. Then, the simulation results are given. Both the theory and the simulation results show that the error probability of selecting two relays is higher than one of the single relay selection.