According to the twice singular value decompositions, the multi-user interference is able to be eliminated by the block diagonalization(BD) precoding algorithm, and the multi-user multiple-input multiple-output(MU-MIMO) channels can be decoupled into multiple independent single -user multiple-input multiple-output(SU-MIMO) channels. But the computational complexity is growing along with the increases of the number of users and the dimensions of the channel matrix. The transmission strategy for the MU-MIMO downlink system based on lattice reduction is presented. The linear detection based on lattice reduction is used to replace the second singular value decomposition of the traditional BD algorithm. Comparing with traditional BD algorithm, the better BER performance and the lower computational complexity can be obtained.