Abstract: Based on an engaging angle function and introducing the solution to conjugate tooth profile of a pair of gears, the geometrical relation between the working profile of a disk cam and that of relevant roller-follower is investigated at a contact point. A direct analytic solution is thus obtained on the basis of engaging angle function, including the working profile of disk cam, pressure angle and radius of curvature. The solution proposed will provide analytically a new simple and efficient approach to the design of cam mechanism especially a reliable mathematic model available to the CAD/CAM of the pairs of disk cam and roller-followers.