This paper reviews the sensing principle, structural design, and temperature measurement performance of fiber-optic high-temperature sensors, as well as recent significant progress in the transition of sensing solutions from glass to crystal fiber. This paper reviews the sensing principle, structural design, and. Optical fiber sensors have the advantages of small size, easy design, corrosion resistance, anti-electromagnetic interfer-ence, and the ability to achieve distributed or quasi-distributed sensing and have broad application prospects for temper-ature sensing in extreme environments. The sensing cavity is mounted at the front end of an extended alumina tube and is illuminated by a collimated light.