A new multi-user two-way transmission network is considered to fully utilize wireless system resource, and ensure transmission reliability, with assistant of an amplify-and-forward relay. In multiple access channel (MAC) phase, signal space alignment technique is employed, which cancel the multi-user interference. In broadcast channel (BC) phase, a new multiple-input multiple-output (MIMO) precoding matrix is designed to reduce the decoding complexity. Simulation result shows the average sum rate performance of the proposed system, and the achievable the degrees of freedom is evaluated.