Vapor liquid equilibria (VLE) of two binary mixtures (ethylene glycol + glycerol and 1,2-propylene glycol + ethylene glycol) were measured at 20Pa. The experimental data satisfy the thermodynamic consistency by Herington method. The vapor phase can be considered as ideal phase, while the non-ideality of the liquid phase was symbolized by Wilson and NRTL activity coefficient models. The experimental data were regressed and correlated by nonlinear least square method of Matlab optimization toolbox. It is found that under the medium vacuum the relative deviations between experimental data and calculated results by the activity coefficient models for low and moderate pressures are larger than 50%. Hence a cubic polynomial regarding the molar composition of liquid phase as the correction of the models was proposed and used in regression to get the interaction parameters. The results showed that the relative deviations between calculated and experimental data are smaller than 1%. The corrected models can provide a calculation basis or data reference for medium vacuum distillation.