Abstract: Hydrodynamic and mass transfer charateristics of a new VST with nozzle-type vapour riser were studied in a circular column of 1.2m with air-water system. The influences of various geometric factors and hydrodynamic conditions upon the tray pressure drop, weeping and the lower limit of gas velocity andentrainment and upper limit of gas velocity were examined. The tray efficiency of the new VST was studied with ethanol-water system and was compared with that of sieve tray. The results are shown as below: 1. The wet pressure drop over the tray is the sum of dry pressure drop and pressure drop caused by gas phase passing through liquid layer. The pressure drops of the new VST with the nozzle-type vapour riser are 40% less than those of conventional VST operating under the same conditions. 2. The amount of weeping can be correlated by the following equation: 3. Entrainment is the upper limit of allowable gas velocity depends on the condition of gas escaping from the slat between cap and tray.