Considering the drag force, virtual mass force and lift force in the Eulerian framework as two interpenetrating phases, three-dimensional flow field in a 0.3 m diameter sieve tray of the fractionating tower were simulated by using the computational fluid dynamics (CFD) STAR－CD v3.26 softerwire. The numerical convergence standard of the computing unstable flow field is the numerical clear liquid height. On the different gas velocities, the numerical results of clear liquid height was in accordance with experimental results. It shows that the method of CFD simulation the flow filed of the liquid and gas phase in the sieve tray of the fractionating tower is doable and credible. The simulation results show that there is the district of the main flow, inverse flow and circulation flow. When clear liquid height increased, the area of inverse flow decreased. There is the interphase momentum exchange of the liquid and gas phase in the sieve tray of the fractionating tower.