In this paper, we propose a new selection mode of 'r, t' for the preconditioner I+C and analyze the convergence performance of the preconditioned AOR iterative method induced by this preconditioner. For a nonsingular M-matrix, we show that the preconditioned AOR iterative method with this choice and the preconditioned methods advised by Evans et al. are all convergent, and that the preconditioned method with the preconditioner I+C has faster convergence speed than the original AOR method. Finally, the limit numerical results are provided to support the obtained results.