The existence of clearance in the joints of mechanisms system is inevitable.The movements of the real mechanism are deftection from the ideal mechanism due to the clearances and the motion accuracv is decreased.The effects of the hinge clearance on the crank and rocker mechanism system are studied.The svstem dynamics equation with clearance is presented.The contact dynamics model is established using the nonlinear equivalent spring-damp model and the friction effect is considered by using Coulomb friction model.Then the models are incorporated into ADAMS,and based on the model,large numbers numeric simulations are made.The regularity of contact forces in clearance are studied in detail.And the effects of clearance size.clearance friction on the mechanism dynamics characteristic are analyzed.The simulation resuhs Can predict the effects of clearance on the mechanism dynamics characteristic preferably.