In this paper, we propose a low complexity opportunistic source-relay selection algorithm based on power allocation for multi-source multi-relay cooperative network. We consider that the channel state information of both the main channels and the wiretap channels to minimize the system secrecy outage probability. First of all, the optimal power allocation factor for each link is given when the total transmission power is limited. Secondly, the optimal selection algorithm is designed based on

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... er allocation and the approximate expression of the secrecy outage probability is derived in the high signal-to-noise ratio regime. Numerical experimental results demonstrate that the system secrecy outage probability of the proposed algorithm is related to the number of relay nodes but has no relation with the number of relay nodes. The proposed a low complexity opportunistic source-relay selection algorithm in this paper not only reduces the computational complexity but also has lower secrecy outage probability compared with the traditional source-relay selection algorithm.