Aimed at the problem of multiple relay selections in satelliteterrestrial cooperative system, a new relay selection scheme based on adaptive genetic algorithm(AGA) is proposed. The proposed scheme assigns one or many relay node models to a source node, and the scheme establishes an optimization model to assign one or more relays, and maximizes the received signaltonoise ratio(SNR) at the destination. The paper analyses the land mobile satellite system(LMS), and the receiver adopts an equalgain combining technique to implement a selective decode and forward (DF) between a source node (the satellite) and a destination node (a terrestrial station). The results show that the scheme based on AGA can improve powerefficiency and the received SNR of 8 dB, compared with the best single scheme under the condition that only one relay node with the maximum SNR is selected. And the proposed scheme can improve timeefficiency of 75%, compared with the exhaustive scheme.