Abstract: The optical constants of diamond-like carbon (DLC) films deposited by UBMS were measured and analyzed with a broadband ellipsometer. Based on the models established previously and the analysis on it, the model structure was analyzed and adjusted according to the film forming characteristic of the DLC film. Considering the effects of surface roughness, film surface, substrate surface and interface factors on the measured result, the surface and the DLC film was divided into two layers during modeling because of its graphitization on the surface, and their effects were approximately processed with the effective media approximation (EMA). The results indicate that the ellipsometric data MSE of DLC films deposited on the silicon substrate by UBMS was reduced from 37.39 to 4.061 by this model. The measurement accuracy was improved.