A main reason that leads to the complex dynamic behaviors of roller chain is the impact during engagement. In this paper, a contact analysis methodology is proposed to study the complex dynamic behaviors of roller chain efficiently. Considering the actual tooth profile, a detection algorithm of roller-sprocket contact was presented. Multi-body dynamics was used to analyze the contact kinematics relationships for purpose of simulating the impact between roller and sprocket precisely. Based on Hertz contact theory, a non-linear contact model of roller-sprocket is developed. Introducing the model to the numerical simulation of a roller chain system, the results validate the effectiveness of the model.