Aiming at the two different installation modes of the screw nut at the condition that the screw is fixed at one end and only supported at another, this paper mainly presents a comparative study about their influences on the load distribution of the ball screw. The different load states of the screw at the two nut installation modes are firstly analyzed qualitatively. Then, a ball screw load distribution model considering the variations of actual contact angle is established. Using the model, the influence laws of the nut installation modes on the the screw’s load distribution, specifically, the normal load and actual contact angle of each steel ball, are quantitatively investigated. The numerical results show that the distributions of the normal load and contact angle both more balanced when the connecting flange of the nut is installed away from the screw’s fixed end. In addition the nut installation have no significant effect on the axial stiffness of ball screw.The conclusion of this study will provide a theoretical guide for reasonable installation or maintenance of ball screws, which may be significant for enhancing the performance of these functional components, as well as prolonging their life.