SiO2 thin films were deposited by ion beam sputtering (IBS) and electron beam evaporation (EB) technologies. The optical constants of SiO2 thin films were fitted by nonlinear least square algorithm. 8 group experiments were designed based on L8(22) orthogonal array. The results show that intermix is the most important factor for the IBS SiO2 thin film while Proe model for the EB SiO2 thin film. The values of MSE evaluation function for IBS SiO2 thin film and EB SiO2 thin film decline 35% and 38% respectively, which shows that the physical models are reasonable and the physical meaning is clear. The method to estimate the effect of different factors was offered, which is meaningful for the analysis of optical constants of thin films.