Abstract: Straight-through and stepped labyrinths are often used in aircraft engine.According to large amounts of experimental data,the empirical formulas of mass flow factor for these two kinds of labyrinth have been provided which are superior to their theoretical formulas due to various corrections.The seal characteristics of the two kinds of labyrinth were compared and analyzed in detail so that their featuers and reasonable conditions of their application were found out.Finally,the new empirical formulas for calculating their critical pressure ratio were derived too.