Using a method of virtual prototype,with the help of the software ADAMS,two versions of Watt's sixbar chain which is the main drive mechanism of slotting machine were modeled,kinematics simulation was also carried out,and taking minimum of the warp of slotting tools during working stroke as optimal objective,the optimum design of the two models on the basis of the preliminary values which were chosen from space model atlas was finished respectively.The merits of the method were shown,and the characteristics of the two versions was analyzed and compared.