The rotary error motion of high speed spindle affects directly the processed workpiece machining precision and product service life. In order to reasonably estimate machining performance of the NC machine tool, the relationship not only between synchronous radial error motion and part roundness, but also asynchronous error motion and surface roughness were analyzed. The rotary error and shift for a certain type of spindle of NC machine tool were measured by using the “Spindle Error Analyzer” developed by Lion Precision Company of the USA. The spindle machining performance is estimated according to the measuring result, which provides reference for practical machining in production.