Aiming at the optimal dividend distribution problem before bankruptcy, in order to realize the optimal distribution of the expected present value of dividend (i.e. the optimal dividend distribution strategy)，in this paper, we consider the cumulative dividend distribution following the Erlang(n) process under the dual model with perturbation, and the optimality of periodic barrier strategy with fixed income when the decision time of dividend distribution is Erlang (2). In order to better explain the influence of other factors on the optimal dividend policy and help us to achieve the optimal dividend policy more accurately, we use the method of numerical simulation to draw the graph between the optimal strategy and other economic factors in the model, and the relationship between them is described. Finally, the corresponding economic explanations are given.