Abstract: This paper presents a method with mixed spectra for analyzing rotational accuracy of spindles, making use of the modified periodogram test combined with dynamic data system modeling. Through dynamic measurement of the spindle radial shaking error and dynamic data processing with this new method, the discrete spectra and continuous spectrum are identified by statistic test, so as to seperate various determinsctic harmonic components. These components include not only the spindle shaking error within a revolution, but also those involving more than one revolution. Being systematic errors they could be corrected in measurement or consequent machining.The method presented in this paper has the advantage of better resolution, higher estimation accuracy and the possibility of correcting these systematic errors on line.