A multi-relay cooperative communication system adopting directive antennas and optimal relay-selection AF cooperative strategy is proposed,and a corresponding formula of system outage probability is derived theoretically.On the basis of the theoretical analysis result,the relationships between the outage probability and the parameters ( namely,the signal-to-noise ratio,the channel fading coefficient,the antenna power gain,the number of relay nodes and the power allocation coefficient) are analyzed by simulations.The results show that the proposed communication system can meet the requirements of military communication for RF stealth,and under the conditions of low signal-to-noise ratio,deep fading channel and limited relay nodes,it has a smaller outage probability in comparison with the cooperative communication system with omnidirectional antennas and the same strategy,which means that the communication reliability is improved.