The AIChE model for Murphree tray efficiency and Colburn's equation for apparent efficiency have become standardized procedures for tray efficiency estimation, although derived under different assumptions. In this paper one-parametric diffusion model has been improved in order to evaluate the entrainment effect and mass transfer in the settling zone. In the case when mass transfer in the settling zone is negligible, the analytical solution obtained for the first time gives the same results as in Locketts numerical solution. It has been found that the presented model improves the accuracy of calculations of the mass transfer parameters in presence of entrainment (overall point efficiency, Peelet number and Murphree tray efficiency) and consequently, of the apparent tray efficiency as well. Derived equations call be converted to the classical AIChE model when the entrainment is neglected.