Abstract: The author studies the preconditioned iterative method for solving the linear system Ax=b.Jae Heon Yun discussed the P=(I+C) to accelerate convergence of SOR iterative method.In this paper, an improved SOR iterative method is employed by using matrix iterative analysis and comparison theorems to solve the large linear system preconditioned based on matrix splitting.The improved method is proved not only to be able to accelerate the SOR iterative method, but also to excel the general preconditioned SOR method.At last, numerical example is given.