The endoscope was first used in the medical field, mainly for the inspection of the internal structure of industrial mechanical equipment. In order to give the endoscope certain protection and not easy to be damaged, according to the powerful hard function of sapphire, most endoscope protection sheets are made by Sapphire process to prevent collision and friction from damaging the endoscope structure during peeping at the mechanical mechanism; The invention of this device by the French doctor desomio has continued to this day. Science and technology have become more and more perfect. After several generations of technological changes, today's achievements have been made. As a result, the concept of endoscope has also undergone congenital changes and opened up a new era of endoscope; During the inspection of the endoscope, because most mechanical environments are high temperature or toxic, and even the inside of mechanical tools is very narrow, it is really inseparable from the sapphire protective sheet to make the endoscope work in such a severe environment. The high temperature has no impact on the sapphire, the poison can't corrode it, and the collision and friction in a narrow space can't damage it, It can be said that this protective film is really a wise choice, which is convenient to record the internal situation of the equipment and find the repair and maintenance parts. Because of its high characteristics, sapphire has been widely used in the application of endoscope protective film, which plays a protective role according to its hard characteristics.