Based on the results of the gasflow field, the droplet size distribution and the droplet initial flow rate distribution on a (phi 300 mm rotating stream tray (RST), a three-dimensional droplet projection trajectory model, and a mass transfer model have been developed. The calculation of the models was carried out by a finite-difference procedure. The predicted results of the tray efficiency agree quite well with the experimental data measured with absorbing NH3 or SO2 in water on a phi 300 mm RST column and with the industrial data from a phi 3600 mm RST column. Meanwhile, the influence of absorbing system and the RST structure on the tray efficiency is discussed.