Abstract: In order to improve the safety level of two-lane highways in mountainous areas,this paper investigated the relationship between highway geometric features and rear-end crash accidents.By using negative binomial generalized models and separating the 139 kilometers highway segment into 94 successive vertical slope units,the statistical software Stata 9.0 was used to evaluate the effects of 8 variables which were based on roadway geometric characteristics of the accidents of rear-end crashes occured from 2003 to 2005 on the mountainous twolane highway in Gansu Province.The variables which influence the accidents of rear-end crashes significantly was accumulated by vertical slope length.The results suggest that there are strong positive relationship between the accidents of rear-end crashes and accumulated vertical length.Therefore avoiding long vertical length as much as possible in highway design is suggested.