A model of drillstring system dynamics was derived based on the drillstring’s Dynamics Equation, System Dynamics Theory and the optimization of absorber’s stiffness and installation site. A numerical calculation approach for solving drillstring system and bit movement was presented according to the drilling parameters. And this paper employed the simulation calculations to analyze and optimize absorber’s stiffness and installation site on different conditions. The results show that the absorber’s stiffness has significant impact on the movement frequencies of bit in the fourth quadrant when the bit next to the borehole wall drills ahead, and absorber has preferable ability of controlling deflection under stiffness for 3950kN/m and 6200kN/m; while the installation site of absorber has acute influence on the bit movement in the first quadrant, the third quadrant and the fourth quadrant, and the optimum position of the absorber is 0.6m distant from the bit. Parameters of absorber’s stiffness and installation site recommended in this study could improve the effectiveness of penetration and are good for controlling deflection and well path.