Abstract: The flow fields of gas and simulating droplet are investigated with the DANTEC 55X laser doppler anemometer on 300mm rotating stream tray (RST). The clarified flow features include: (1)Axisymmetrical flow. (2)The tangential velocity ut distribution is composed of an inner forced vortex and an outer quasi-free vortex. (3) The upflow (axial velocity uz >0) is mainly in the annular cross-sectional area greater than 1 / 2 radius, and a downflow occurs in the area over the liquid receiving-distributing disk. (4)In the main two-phase contacting area, ut and uz are found to be well correlated as equations 1 and 2 respectively. (5)The radial velocity is about one-tenth of ut or uz. The respective purposes of the internally and externally-oriented trays in design can be established from the two-phase flow feadtures. Using a two-equation k-ε. model and a finite-difference procedure, a numerical model for calculating the turbulence flow on RST is also given in this paper. The computed velocities and pressures are compared with the experimental data, and satisfactory agreement is obtained.