Abstract: In order to improve the security and reliability of wireless transmission system, a bidirectional multi-hop relay network model based on decode transmit is constructed in the multi-link communication network with eavesdroppers. The relay link selection strategy was proposed, and the exact expression of the system security outage probability was derived under the Rayleigh fading channel. The effects of SNR, relay number and distance factor on the security outage probability of the system were analyzed by simulation. Simulation results show that the secure outage performance under the optimal relay selection strategy is better than that under the random relay selection strategy. Compared with unidirectional multi-hop relay network, there is little difference in secure outage performance between the two networks, while bidirectional transmission improves channel utilization and transmission efficiency.