Abstract: Abstract: Ball screw mechanism is one of the key parts in mechanical and electronic products especially in precision machineries due to its high transmission efficiency, long service life and high precision, high carrying capacity and positioning accuracy, which is determined by the contact angle formed between nut and screw. Aimed at the current problems in universal and limited application, which resulted from the specific structure parameters, this paper establishes the relationship between contact angle and ball screw's structure parameters, as well as the model of the dynamic contact angle of ball screw mechanism combined with the geometric parameters of the ball and the raceway between nut and screw. The relationship between force and deformation in ball and raceway is got by using the Hertz contact theory, which is used to solve the stiffness in contact area between screw and nut. The relationship between ball's rotation and revolution speed and screw's rotation speed is got by using the raceway control theory, which is used to solve the centrifugal force and gyroscopic moment formed under working conditions. The structural model of the nonlinear equations of contact angle is got, in which the variable includes clearance, nominal diameter, ball diameter, helix angle and ball number. The solving procedure of dynamic contact angle is given based on the Newton-Raphson method. The influence of structure parameters on contact angle of ball screw mechanism under different working conditions is studied through the example analysis, and verified by contrasting the influence of ball screw's rotational speed on contact angles with a specific structure. The results show that the inner contact angles in screw raceway are always greater than the external angles in nut raceway under working conditions. The inner contact angles increase with the increasing of screw's rotational speed, and in contrast, the external contact angles decrease. Both the values of inner contact angles and external contact angles increase with the load increasing under the low speed working condition, but the difference of the 2 values decreases. Under the working condition with high speed and low load, the inner contact angle decreases at first and then increases with the load increasing, while the external contact angle only increases, and the difference value of them still decreases. As for the influence of structure parameters on contact angles, the inner contact angle is always bigger than the external contact angle; both the inner contact angle and the external contact angle increase by about 7° while the clearance between ball and raceway increases by 0.1 mm; increasing the nominal diameter can lead to an increase on the inner contact angle and a decrease on the external contact angle; the ball's diameter and number have the familiar influence on the contact angle, the external contact angle can decrease with the increasing of the ball's diameter or number, but the inner contact angle decreases at first and then increases with the increasing of the ball's diameter or number; the helix angle has little influence on both the inner contact angle and the external contact angle, and the change values of both contact angles are less than 0.006° when the helix angle increases by 1°. Research results would provide the reference for the optimal design, dynamic characteristics analysis and accuracy improvement of ball screw mechanism.