Three-phase packed distillation has been so far relatively poorly understood. Hence, a Substantial mass transfer model describing the (vapor-liquid-liquid) three-phase flow in packed column is proposed to explore the essence of three-phase distillation. The model enables, for the first time, rigorous computation of all the interphase transfer parameters oil the basis of a thorough consideration of the unique How behaviors (Such as film breakup, rivulet-flow, Surface variation, etc.) Caused by the second liquid. The derived theoretical mass transfer model has been incorporated into the three-phase nonequilibrium Simulation. Moreover, comprehensive experimental investigations have been carried Out using two laboratory-scale columns, and four different packings (Montz-Pak B1-350, Rombopak 9M, Raschig Super-Ring 0.3, and Sulzer Optiflow C.36) were considered. The derived experimental database, covering a wide range of load conditions, is used for flow pattern identification and model validation. For the Studied n-butanol/water/n-propanol system, it is revealed that the flow pattern of file second liquid (aqueous phase) could play a critical role in the system performance. When the second liquid flows below the first liquid film, it will enlarge the interfacial area and enhance the vapor-liquid mass transfer; when the second liquid flows above the first liquid film, it will reduce the interfacial area and degrade the mass transfer. This fundamental flow behavior may essentially result in the discrepancy existing in the highly variable separation efficiencies in three-phase packed columns.