In this paper, the auto door-handle was taken for an example, the quantitative analysis of the processing parameters (including melt temperature, shot size, delay time and gas pressure) on gas penetration in GAIM process was introduced using the method of orthogonality and computer-aided engineering. The effort in this article is aimed at the effect extent and trend of the four parameters on the molding result. Through the study, the main achievements are as follows: In short shot process for thick-wall parts, the shot size is the most significant factor on the molding result, the delay time is the second and the gas pressure is the last one. The length of gas penetration will increase with the reduction of shot size and delay time, or with the increasing of melt temperature and gas pressure. Then the optimization of the process parameters on the door handle was carried out.