Abstract: Network Coding has been investigated extensively in bi-directional multi-relay system and can improve the throughput of bi-directional multi-relay system effectually. Firstly two outage probability expressions of bi-directional multi-relay system on independent orthogonal channel and multiple access channel with decode-and-forward based on network coding are given in this paper and theory analysis is proved correct by Monte Carlo simulation. Secondly we analyze the system average outage performance at different situation of different power allocation coefficient，SNR and the number of relay，indicating the inherent relationship between power allocation coefficient and total system power as well as the number of relay. Simulation results indicate that optimal system outage performances of bi-directional multi-relay system on the two channels are attained when power allocation coefficient is chosen in ，and we can see that outage performance of the system on multiple access channel is better than the independent orthogonal channel.