An early-warning apparatus for health detection of a servo motor and a method for operating the same are applied to estimate vibration phenomenon of a CNC tool machine. First, a vibration signal is produced through a vibration detecting unit. Afterward, the vibration signal is sequentially sent to a data buffer. Afterward, the vibration signal is transformed in time and frequency domains through a time-frequency transforming unit. Finally, a deterioration index is calculated through a deterioration index calculating unit to obtain a health index which is calculated through a health index calculating unit. Therefore, the build-in vibration detecting unit is provided to dispense with additional external sensors. Furthermore, the vibration phenomenon of the servo motor of the CNC tool machine is estimated according to the health index, thus analyzing non-linear and non-stationary characteristics of the estimated vibration phenomenon.