A medical electric drill includes a drilling head, a microprocessor, a pressure sensor unit, a torque sensor unit and a gravity sensor unit. The drilling head is for drilling a bone. The microprocessor is signally connected to the drilling head for calculating a displacement of the drill. The pressure sensor unit is for detecting a pressure change and provides a pressure change signal to the microprocessor. The torque sensor unit is for detecting a torque change and provides a torque change signal to the microprocessor. The gravity sensor unit is for detecting an acceleration variation of the drilling head and provides an acceleration voltage signal to the microprocessor. The microprocessor determines a work period of drilling the bone according to the pressure change signal and the torque change signal, and then the microprocessor calculates the displacement of the drilling head by using the acceleration voltage signal during the work period.
