In car refinishing, the paint film characteristics of clear coat play an important role in appearance quality. Thus, Primarily in this research, the variance of brightness with the change of the thickness of paint film is investigated. Besides, as changing the thickness of paint film, the correlation between surface leveling(which is one of appearance characteristics) is investigated in this research. Throughout this investigation, we come to know that the increase of clear coat paint film thickness leads the improvement of appearance characteristics within specific range of thickness. Furthermore, the fact that too thick paint film does not increase the brightness or appearance characteristic any more is known. The optimum thickness of clear coat film for the best and appearance characteristics is derived from this research and more efficient way of determining optimum thickness of paint film is found. Particularly, haze value and waviness have more influence on vividness than brightness. Throughout all experiments, the appearance characteristics are much better at painted horizontally than vertically. These results are derived due to the facts that to obtain the same paint film thickness at painted vertically with painted horizontally is difficult and the way of vertical painting is different from horizontal painting. Therefore, the improvement of vertical painting and horizontal painting are required.