Abstract: A new mathematical model of mixing pool type is proposed to simulated the fluid flow and mass transfer behavior in a large tray. In the proposed model, the whole tray deck is divided into a number of square (or rectangular) compartments or mixing pools, each of which is assigned to have adjustable flow and backmixing in both z (along the main flow path) and w (perpendicular to the main flow path) directions. The chief features of present model are: (1)It is a two dimensional model instead of usual one dimensional so that more complicated actual flowing condition obtained from hydrodynamic study in a large tray can be closely simulated by adjusting the flow among mixing pools in both z and w directions. (2)Since backmixing is taken into account, the number of mixing pools in a tray can be fixed instead of varied as in conventional mixing pool model;thus, the application of matrix computation is possible. (3) The present model can be reduced to other tray models depending on the number of mixing pools to be chosen in each direction. The application of present model to predict the liquid phase concentration profiles and Murphree efficiencies in a tray with complicated flow pattern and velocity distribution as we observe in our experimental study are demonstrated. The effects of liquid flow rate, non-uniform velocity field, directional splashing and subsidiary flow are also investigated and discussed.