Abstract: A fixing device and an installation tool and a fixing method of the cranial flap, wherein the installation tool comprises a driving part, a loading part and an over torque protection mechanism disposed between the driving part and the loading part, the driving part drives the loading part to rotate by the over torque protection mechanism, the loading part is used for tightening the cranial flap fixation device, when the torque of the driving part acting on the over torque protection mechanism is larger than the threshold value, the over torque protection mechanism will be separated from the driving part and/or the loading part. The present invention not only effectively improves the installation and disassembly efficiency of the installation tool, but also eliminates hidden safety hazards caused by uncertainties caused by human factors in the tightening process, significantly improves the safety of the installation process.