Abstract: Aiming at the rippling on CNC lathe boring that inspecting step by step and confirming the rippling source preliminarily. Applying the float chuck fixture to improve the spindle rigidity and decrease the depth of the lathe tool indirectly which approve the rippling and spindle irrelevantly. Applying the envelope demodulation analysis method, by apply the LC-810 vibration signal acquisition analyzer to pick the vibration signal on front-end and back-end of spindle, the average data at 22.37 Hz and 45.94 Hz, which approach to the 22.127 Hz and 44.792 Hz of NN3048 and NU1038 bearing fault character frequency. Through the dismantle bearing and boring test that testify envelope demodulation analysis method is available on bearing fault diagnose. The result is the abrasion between NN3048 bearing and NU1038 outer race is the source of rippling, the theory and test result is consistent.