Abstract: In automotive body assembly, gap and flushness is one of the most important quality factors. An optimizing method based on fractional Hausdorff distance was proposed to improve the gap and flushness of front end, the area among the hood, headlight, bumper and fender. The weighted sum of fractional Hausdorff distances among the corresponding regions was employed as the optimal matching function. It could find the global optimal position by using the genetic algorithm. The effectiveness of the method was demonstrated by two practical examples. At the same time this method possesses guiding effects on tolerance design of front end.