Dry CVT(Continuously variable transmission) consists of a driving pulley and a driven pulley joined by rubber V-belt. Each pulley consists of a fixed flange and a movable flange. The movable flange of the driving pulley has the centrifugal roller and a ramp plate in the flange. In this study, the formula with respect to relationship between a driving pulley and a driven pulley was derived, based on theoretical investigation about Dry CVT of a common and practical auto-bicycle(125cc). Also, the axial forces on the driving pulley and the driven pulley were analyzed.