In order to reduce the pollutants of diesel exhaust, DOC, DPF, SCR, AOC, etc. are mainly used for off-machine after-treatment technology, but it is difficult to meet the requirements of the newest emission regulations simply by relying on a certain aftertreatment technology. Therefore, the use of integrated aftertreatment system has become a necessary choice. In this paper, the research object is one of the integrated aftertreatment systems (DOC+DPF+ SCR+AOC). Then, the effects of the different exhaust parameters, the different structural parameters and different chemical reaction parameters on the catalytic conversion efficiency of NOx, HC, CO, and PM are studied.