In order to replace trial-and-error methods with more systematic procedures which can reduce or eliminate exterior styling defects of automobile such as micro deformation, we simulated the mechanism of micro deformation that occurs during the painting process. We studied the characteristics of mastic sealer which was regarded to have the most important effect on the micro deformation. Also we established a stiffness scanning procedure to identify the structural characteristics of the roof assembly. Material parameters of the cured mastic sealer were obtained by shear test and the corresponding analysis. Through stiffness scanning, the load-stroke curves for the main locations of the roof were obtained. We numerically modeled the automobile roof structure with measured material parameters of mastic sealer and virtual elastic materials at specific joints. Virtual elastic material was introduced to minimize the difference between the computations and the measurements of load-stroke curves that may not be simulated practically with various reasons. The validity of the foam, the driving force, the elastic models of mastic sealer and the structural analysis procedures was verified by comparing the location of the actual micro deformation after oven process line and the computation results. It was concluded that the micro deformation on the roof could be numerically simulated with proper material and numerical models and they were utilized as tools for eliminating defects.