Abstract: The multi-body dynamic simulation widely used in the current research of the toggle clamping unit of injection molding machine was failed to consider the influence of the elastic strain in the clamping process，and therefore met difficulty to explain the motion characteristic of the moving platen. Based on elasticity theory, a mathematical model of the clamping force was formulated via deformation analysis of mode locked state on the clamping mechanism, the relationship among the joint mechanism stiffness，institutions deformation, and clamping force was revealed. The simulation was carried out using rigid-flexible coupled dynamic mode and rigid mold，the dynamic template speed and displacement curve were obtained. The motion characteristic of the moving platen and the influence on the quality of molding products were explored.