Abstract: Needle roller bearings are used to support heavy radial loads. If the rollers and raceways of the bearings have straight generatrices of motion, then notwithstanding relatively light loading, edge effects tend to occur. To avoid this phenomenon, needle rollers are usually crowned. In this paper, the effect of the grinding undercut on the longitudinal pressure distribution of the needle rollers with Lundberg' s profile, which are used in the needle roller bearings with machined guide ribs,is disscussed. The analyses show that the width of grinding undercut must be considered in determining the crown drop of the needle rollers. It is a very important discovery in the study. Based on the Lundberg' s equation and the numerical calculation of three-dimensional elastic contact problems of finite length,a new numerical method for the crowm drop evaluation considered the effect of the grinding undercut is developed according to the discovery. The method used makes it possible to profile the needle rollers axially until the longitudinal pressure distribution is neither any "edge effects "nor high pressure concentration at the center. The method is useful as a guide to design not only the needle rollers, but also other rollers used in the roller bearings with the same kind of structure.