The threedimensional steady flow in shaft seal of PT1230 mediumpressure cryogenic turboexpander was simulated by computational dynamics fluid method,and the sealing performances of 12 sealing solution,which were made up of four tooth profiles (rectangular tooth,hook tooth,two triangle teeth with different pitch) and three intakeexhaust system were studded.The results show that tooth shape has great influence on the leakage,among them triangle tooth with larger pitch has the strongest sealing property due to its big seal chamber and full throttling expansion,but the axial length of the sealing is increased.The sealing effectiveness of tooth sealing is mainly dependent on pitch between the tip and endwall,so that shortening this pitch can increase pressure gradient and enhance sealing effect.For the shaft seals with four different tooth profiles,the shaft seal with the intake and exhaust mode of single inlet and double seal gas outlet has the maximum leakage,and the shaft seal with the mode of single seal gas inout has the smallest leakage.The computational results can provide the necessary reference for rational design of seal open position,appropriate selection of tooth length and improvement of sealing effect.