With the development of mechanisms for high speed and high precision, the dynamics performance of mechanisms designed by pure rigid body dynamics theory can’t meet the requirements. This study proposes a flexible dynamics model of a high-speed cam mechanism with an oscillating roller follower. Based on Hertz line contact theory and coefficient of restitution, the contact force between cam and roller is obtained. Applied the Finite Element Method, a flexible model of the oscillating follower with uniform cross-section is built. The results of numerical analysis show the structural elastic deformation of the follower has distinct effects on the angular displacement at high speed.