In order to enhance the relay's performance, and use the resource efficiently, a multiple input multiple output (MIMO) relay selection scheme based on amplify-and-forward (AF) cooperative system is proposed. In this paper, we consider the diversity combining at MIMO relays, and provide a condition to maximize the overall output signal-to-noise ratio (SNR). In this condition, the ineffective relays will be excluded in sequence from the cooperation; therefore the unused relays can be reallocated to other users. In the proposed system model, we use the maximal ratio combining (MRC) at MIMO relay, and employ the best channels from each relay to the destination. Each relay transmits the signal with identical power; meanwhile, the total power allocated to the source and the selected relays is set by suboptimal distribution. Simulation results indicate that the effect of bit error rate (BER) through the relay selection is similar to the scheme which applies all relays, but the amounts of used relay decreased. And the proposed MIMO relay scheme is superior to the single input single output (SISO) one about 7dB. Therefore, the relay resource could be used more efficiently than we employ all relay. In addition, the MIMO relay scheme can enhance the relay's performance.