Abstract: With a few exceptions of synchronous motor servometers and microwave meters used in imported pressure tanks, level sight glasses have been continuously used for level measurement of LG tanks and other pressure tanks in China, though having meny disadvantages such as frequent leakage and big error. Optical fiber level gage for special tank, a new product made from the techniques of optical sensing and computer, is characterised by fire prevention, explosion-proof, anti-electromagnetic interference, high accuracy, easy installation and adjustment, reliable operation and corrosion resistance. Introduced in this paper are the principle, structure, specifications, installation and application of the GY——9200 type optical fiber level gage. The precision of the instrument, made on the basis of the mechanical initial point of instrument rather than level sight glass, is calculated by comparing the output and input LG masses with the mass measured by the gage. This kind of instrument realised automatic measurement of the liquid level in pressure tanks.