In order to effectively improve the spectrum efficiency of the Multiple-Input Multiple-Output（MIMO）system and reduce the complexity of the algorithm

this paper proposes a matrix decomposition algorithm based on iterative method.First

the analog precoding matrix is initialized and the optimal precoding matrix is obtained.Then the digital precoding matrix is obtained by simulating the precoding matrix and the optimal precoding matrix

and the analog precoding matrix is updated by extracting the phase information in the digital precoding matrix.The updated simulation matrix updates the digital matrix and finally iterates through alternating iterations until convergence.The simulation results show that it has lower complexity and better performance

which is closer to the pure digital precoding performance.