One of the important factors resulting in the performances of the machinery is its dynamic characteristics. The spindle assembly is one of the usual parts of NC machine tool, so its dynamic-static characteristics will affect the performances of machine tool. The study is based on a NC machine tool produced by a certain plant of machine tools. The finite element dynamic analysis model of spindle assembly was developed by introducing two or three groups of circumferential spring damper elements which are arrange at different angle around the spindle, and the effect of different supporting conditions and different arrange angle on the modal analysis of the spindle assembly were discussed. The finite element analysis on spindle and spindle assembly has been made to confirm its dynamic characteristics. Then the finite element analysis models are validated by some experiments.