Abstract: A method includes steps of: performing preparation-phase measurements on a spindle of a machine tool to generate normal-condition signals; establishing a reference model based on the normal-condition signals; generating abnormal-condition signals based on the reference model and a preset damage value; utilizing principal components analysis (PCA) to characterize the normal-condition and abnormal-condition signals to obtain normal and abnormal probabilistic models, determining normal-condition and abnormal-condition reference curves based on the normal and abnormal probabilistic models; determining an alert-triggering line based on the abnormal-condition reference curve; determining a permissible range between the alert-triggering line and the normal-condition reference curve; and generating a warning signal when it is determined that a detection value falls outside of the permissible range, wherein the detection value is obtained based on application-phase measurements performed on the spindle.