In this work, the molecular interaction volume model (MIVM) was reasonably simplified. The values of the first coordination numbers (Z(i) and Z(j)) were set as 10, and the molar volume of the component i in the liquid state (V-mi) was replaced by its molar volume in the solid state (V-i). The activities of the components of Pb-based alloys (Pb-Sn, Pb-Sb, Pb-Ag, Pb-Cu, Pb-Bi, and Pb-Cd) were predicted by using the simplified MIVM (SMIVM). The prediction deviations of SMIVM were overall smaller than those of MIVM, indicating that the simplification of the MIVM is reasonable and the SMIVM is reliable for predicting the activities of the components of Pb-based alloys. The biggest advantage of the SMIVM lies in its simplicity in calculation and higher prediction accuracy than MIVM. Vapor-liquid equilibria (VLE) phase diagrams for the Pb-Sn, Pb-Sb, Pb-Cu, Pb-Ag, and Pb-Bi alloy systems in vacuum distillation were calculated based on the SMIVM and VLE theory. The experimental VLE data deviated from the calculated results to a certain extent This study summarizes the shortcomings of current research on the VLE of alloy systems for future research and development. (C) 2018 Published by Elsevier B.V.