Abstract: In order to eligibly choose seal on centrifugal compressor shaft to prevent poisonous gas from leaking into atmosphere, four common seal types are analyzed contrastively.They are labyrinth seal, floating ring seal, mechanical contact seal and dry gas seal.Labyrinth seal is rarely used alone because it will induce substantial leakage when pressure is high.So it is suitable for lower pressure situation.Floating ring seal and mechanical contact seal require seal oil and corresponding control system.The two kinds of shaft seal have several disadvantages, for example, complicated control system, highly maintenance cost, serious contamination, more power consumption and lower stability.Dry gas seal, which is end-face seal with lower leakage, is gas-lubricated without contacting with the shaft.Therefore, it needs fewer operation cost, has rare contamination and long lifespan.Accordingly, dry gas seal is an optimal form of centrifugal compressor shaft seal.The cost and contamination will be greatly reduced by using dry gas seal.