Abstract:The past and now known or non ascertain information of spindle rotation accuracy of CNC lathe, regarded as a gray system. For five of the same type CNC lathe, radial motion errors and axial motion errors of the spindle, and motion errors of chuck face were detected at regular intervals. These errors constituted the raw data equally spaced data series. Model of Grey System GM(1,1) was established. Differential equations of gray system were solved. The result shows that correction by means of residual model improves accuracy. And the modified GM(1, 1) model can be used to forecast the life of spindle rotation accuracy of CNC lathe, which provides evidence for maintenance cycle for the latter, replacement of spindle bearings and recovery of spindle rotation accuracy on CNC lathe.