Abstract: In order to reveal the variation characteristics of ballast bed lateral resistance, a three-dimensional model for ballast bed and sleeper was established based on the discrete element method. The effects of important factors of ballast bed section dimension, such as ballast bed slope grade, thickness, top width and shoulder height, were investigated, and proportions of lateral resistance shared by sleeper base, crib and shoulder were analyzed. The research results indicate that when slope grade changes from the ratio of 1 to 1.50 to the ratio of 1 to 1.85, lateral resistance varies from 10.315 to 16.475 kN, and if slope grade equals the ratio of 1 to 1.65 or smaller, lateral resistance can satisfy 12 kN per sleeper. When top width increases from 3.0 to 3.8 m, lateral resistance varies from 10.205 to 15.715 kN, and if top width is 3.4 m or wider, lateral resistance can satisfy 12 kN per sleeper. Lateral resistance increases with the decline of slope grade and the increasement of top width, shoulder resistance increases significantly as a result of the increasement of shoulder ballast. When ballast bed thickness increases from 200 to 400 mm, lateral resistance varies from 9.156 to 15.684 kN; ballast bed drags based on different layers when the sleeper moves laterally; and base resistance increases along with the increasement of ballast bed thickness, and if ballast bed thickness is 300 mm or larger, lateral resistance can satisfy 12 kN per sleeper. When shoulder height increases from 0 to 180 mm, shoulder resistance varies from 2.010 to 5.203 kN and lateral resistance varies from 9.526 to 15.257 kN. Shoulder height affects lateral resistance significantly, and if shoulder height is 120 mm or higher, lateral resistance can satisfy 12 kN per sleeper.