Recently, the cooperative diversity systems, based on the distributed space-time coding (DSTC), have been presented to provide the spatial diversity gain in the wireless networks. Although the performance of DSTC cooperative diversity systems is quite attractive in terms of the link performance, the complexity and the power consumption at each node are the main practical issues for the deployment of the systems, in particular, when the number of nodes is large. In this paper, we propose the suboptimal relay selection algorithm where a predetermined threshold is set both at the relay node and the destination node, and the node selection is performed only when the signal quality of either relay node or destination node is below a predetermined threshold, which has less complexity than the opportunistic relaying in  while satisfying the required performance. We provide the closed-form expression of statistics of the output SNR and study the complexity of the proposed scheme. Based on our analytical results we show several selected numerical examples to show the efficiency of our proposed schemes.