The modified molecular interaction volume model (M-MIVM) was used to calculate the activity values and their deviations from experimental data for Ag−Cu and Ag−Sb binary alloys. Subsequently, theoretical vapor−liquid equilibrium phase diagrams (T−x−y and p−x−y) were plotted via combining M-MIVM and vacuum theory. The vapor−liquid phase equilibrium (VLE) experiments were conducted on the Ag−Cu alloy at 1500−1560 K and 10−15 Pa and Ag−Sb alloys at 950−1350 K and 10 Pa. The results showed that the average relative deviation and average standard deviation of activity were lower than 5% and 0.02, respectively. A comparison of theoretical and experiment results for VLE revealed that the simulated data on the T−x−y diagram were well consistent with experimental values. Therefore, the VLE phase diagrams can serve as a guide in vacuum separation experiments and industrial production for Ag−Cu and Ag−Sb binary alloys.