In order to get the dynamic characteristics of a ball screw reliability teat bench,the finite element dynamics modeling of the test bench is carried out. Aiming at the specific on the feature that ball screw system has too much rolling joints and the Finite Element Method（ FEM） can’t simulate it well,the Hertz contact theory is used to calculate the stiffness of ball screw joint,rolling guide joint and the bearing joint. Then,the improved dynamics model is established. By using impact test method,the modal test of the test bench is carried out,then a contrast between the improved dynamics model and the data obtained from the experiment is carried out. The maximum modal frequency error is no more than 4% which verified the correctness of model.The dynamics basis for the further ball screw faulty diagnosis and life prediction is provide by this model.