The insulator, in ramjet's afterburning chamber, works in a serious condition. Its ablation model has been established based on two-phase-flow model. With this model, a ramjet interior flow field has been numerically simulated under a certain working condition. In order to improve insulator performance, two methods has been argued. Compared with the numerical simulation results of these methods, it is found that the distance between two neighbor inlets affects ablation rate and this makes the insulator by side of backward inlet be more seriously ablated than insulator around forward inlet. On the other side, the numerical simulation result shows that a certain velocity enhancement of air would alleviate the insulator ablation.