Diamond relay network is a kind of efficient cooperative net- work, in which the source user selects two neighbors as relays and cooperates with both of them. In our previous work, we have studied its transmission rates for different coding and relaying schemes and proved that the performance of SRP scheme (Spatial Reuse Pattern) is better than others. To fur- ther improve the performance, we incorporated the oppor- tunistic scheduling and studied how to use buffers adapted to the time varying Rayleigh fading channel. However, the position information of users has not been considered yet which actually has a great infuence on the performance of the diamond relay channel. Thus, in this paper, it is the first time that we study how to select the position of two relays to guarantee the performance of the throughput and delay constraint. This study facilitates the practical application of diamond relay networks since the source user knows thatfrom where selecting neighbors as relays will bring nice per- formance. Finally, the simulation results confirm our analysis and some interesting illustrations show much novelty.