Abstract Dimensional deviations in the cage pocket of a roller bearing can significantly affect the bearing’s dynamic performance, directly determining the positional stability of the roller. These deviations can result in roller misalignment, increasing friction and wear. Deviations arise from machining errors and deformation during motion, etc. A dynamic model of a cylindrical roller bearing that accounts for cage flexibility was developed to explore the impact of deviations. The flexible cage provides a more realistic representation compared to the rigid cage. The effects of deviations in the length and width of the cage pocket on the bearing’s dynamic behavior were analyzed, and the results show that deviations in cage pocket dimensions lead to notable changes in bearing dynamics. Specifically, when the length deviation is negative and increasing, the amplitude of cage motion decreases, while both transitional and rotational speeds rise. It also causes greater fluctuations in the rotational speeds of the inner ring and rollers. Conversely, the cage’s equivalent stress and the contact load decrease and the amplitude of cage motion increases with increases in width deviation. Keywords: pocket; dimensional deviation; cylindrical roller bearings; dynamic characteristics