For up?link multi?user multiple?input multiple?output relay systems, with the aim of minimizing the bit error rate, a linear precoding scheme design is proposed based on the minimum mean?squared error (MMSE) rule in the presence of the feedback delay and channel estimation error. The proposed precoding algorithm decomposes the constrained optimization problem into three sub?convex optimization problems that are solved separately. The transmitter equipped with single antenna is subject to independent distribution, and it can be assumed that the precoding matrix is a diagonal matrix. The convex optimization problem of relay matrix is transformed into semi?definite programming problem (SDP), which can be solved by CVX toolbox. The equalizer matrix can be introduced by the gradient?based line search algorithms. Then the optimal solution is obtained by using joint iteration. The simulation results show that the proposed scheme can achieve better system performance.