Numerical simulation of the injection molding process of the outer panel of the automotive plastic rear door and mold design is presented here. CATIA is used to design the original automotive steel structure. In order to efficiently design the panels; finite element analysis is used to verify whether the designed parts meet the mechanical properties requirements such as light weight, low fuel consumption, short production cycle, strong modeling design, high corrosion resistance and good recovery. To simulate the injection molding process, CAE software such as ANSYS and HYPERWORKS are used to analyze the back door of the selected material. After the numerical analysis, suitable material is selected, so that the modal and thermodynamic properties of the product could be satisfied as well as improved. In this paper, UG is used to design the convex and concave mold for the injection molding of the automobile’s plastic back door panel. Combined with the characteristics of the parts and the design requirements of the injection mold, the multi-scheme design of the pouring and cooling system is carried out. By comparing the effects of different gating and cooling systems on injection molding, the best gating and cooling system is selected.