A method of controlling automatic stop of a surgical drill 1) uses a smart module to receive instantaneous electrical signals of a driving device coupled to the surgical drill； 2) sets the length of a unit time, and sets the average of all instantaneous electrical signals received in a unit time as a reference electrical signal； and 3) compares the instantaneous electrical signal with the reference electrical signal. When the instantaneous electrical signal experiences a step drop with respect to the reference electrical signal, the smart module sends a stop command to the driving device to stop the operation of the driving device.
