An evaluating method of gas velocity distributions along the tray deck is reliably formulated in this paper that derived from sum model of the pressure drop combined with pressure balance on trays. In order to validate the formula

a case study is presented to illustrate the method. The experiment program was carried out in the 6400 mm×800 mm rectangular simulators with air/water system in which two-pass valve trays were divided uniformly into 16 zones（8 zones in every pass）. Pressure drops (dry and total) and liquid hold-up in every zone along tray decks were measured. The model can well characterize and predict the local gas rate distribution in each zone along tray decks on large scale trays within reliably accuracy based on the experiments data of pressure drop and liquid holdup.