Abstract: The dynamic characteristics of the spindle box have important influence on the vibration performance of the whole vertical machining center. In order to study the dynamic characteristics of the spindle box of vertical machining center after adopted the welding parts instead of the casting, this paper got the first six order natural frequencies and modal shapes of the casting and welding spindle box of vertical machining center by means of the finite element method and the experimental method. Comparing the results obtained from this two methods, the validity of the finite element analysis model was verified. The results show that the damping ratios of the two kinds of spindle box are close, but every natural frequency of the welding spindle box is higher than that of the casting one. Moreover, the natural frequencies of the casting spindle box is closer to the common working frequency of the machine tool's spindle, while the welding's is far away from this frequency. Therefore, in terms of the commonly used spindle speed, the dynamic performance of the welding spindle box is better than that of the casting one.