Floating oil seal is often used in planetary reducer of the moving part of construction machinery to seal the end face of the part dynamically. Because of its high reliability, it is also used as the dynamic seal of the output shaft of the bucket wheel of the dredger in recent years. It is a non-contact seal. Its structure is to maintain a certain gap between the floating ring and the rotating shaft, and it can float freely, but it can not rotate with the rotating shaft, only for the radial sliding floating, and under the action of gravity, it keeps a certain eccentricity with the shaft center. The sealing of fluid medium leakage is realized effectively. It has the advantages of stable sealing performance, reliability and long service life. It is especially suitable for the sealing of gas medium in centrifugal compressor, and it can also achieve the sealing of flammable, explosive, toxic and precious gas medium without leakage to the atmospheric environment.