In order to research the dynamic characteristics of spindle-bearing system, the spindle system of one type of precision horizontal machining center is taken as the object. The stiffness of the bearings for spindle support was set to the values measured in eccentricity mass excitation tests, and the spindle was finite element modeled by using Timoshenko beam elements. The influence of spindle centrifugal effect and bearing preload on the dynamic performance of the spindle-bearing system were analyzed systematically, and were verified by tests. The results show that increasing the preload can effectively improve the stiffness of the spindle bearings as well as the dynamic performance of the spindle. At the same time, it is proved that to calculate the stiffness of spindle bearings by using Finite Element Method (FEM) is an effective method.