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In this paper, a two-tier network coding (TNC) scheme is proposed for the multi-user multi-relay transmission scenarios. Specifically, TNC is conducted at each individual relay, where two groups of source messages are combined into one network codeword that is forwarded to dual destinations. Finally, two groups of source messages are jointly recovered from different network codewords at the destinations. Both analytical and simulation results demonstrate that the proposed scheme outperforms the current state of art in terms of the energy efficiency (EE). In addition, the impacts of multiple parameters, including the number of users, SNR and relay locations on the average EE have been demonstrated, which provide valuable insights for the system designs of future wireless networks.