To design a machine tool successfully, its essential parts should be analyzed and evaluated after design but before prototype being made. The spindle assembly is one of the most essential parts of high speed machine tool, so how the dynamic characteristics of the spindle assembly affect the performance of high speed NC machine tool are of great significance and should be studied. This paper’s research is based on a high speed machine tool manufactured by some plant. The finite element analysis model of the spindle assembly of the high speed machine tool was developed by taking the advantage of the spring-damper element to simulate the bearing supports. The modal analysis was made to confirm the dynamic characteristics of the spindle assembly, and the results were compared with the testing ones.