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The principle of initial parameter method to establish the initial parameter matrix equation for force and displacement of ball screw was explored. The structural characters, including boundary condition, force balance and displacement compatibility in support point were used to achieve initial parameter values. As a result, force and displacement of every point on ball screw could be obtained. Meanwhile, an identification method of the radial rigidity of support point was put forward. The identification models of radial rigidity were built by analyzing the amplitude changes of ball screw under some load affection employing the knowledge of mechanical vibration and material mechanics. The results are in good agreement with the results obtained by the available experiments.