Abstract: The clearances that exist in the mechanism will lead to the motion deviating from ideal movements, meanwhile reducing the kinetic accuracy of mechanical. In order to investigate the output motion error of the offset slider-crank mechanism with clearances, the dynamic equation and virtual prototype model is established based on the impact-pair model and the kinematics characters of the mechanism are analyzed. With the established model, the optimization of the design parameters is proposed to recover the minimum value of the error. The result can predict the dynamic characteristics of mechanism and effective improve the motion precision of the mechanism.