Vacuum glazing is a new type of green building material with great heat preservation, thermal insulation and noise reduction performance. COMSOL Multiphysics 5.6 was utilized to establish the physics models to explore the performance of vacuum glazing with different specifications and simulate the application of different glasses in energy-saving buildings in this study. The results show that the thermal insulation performance of vacuum glazing with size of 500 mm × 500 mm is better than that of 200 mm × 200 mm and 100 mm × 100 mm. With the size increasing, the area of the vacuum gap becomes larger, whereas the edge sealing layer occupies a smaller percentage of the surface area of the whole vacuum glazing. Therefore, the effect of the edge sealing layer on the heat transfer of the vacuum glazing is reduced, and the thermal insulation performance of vacuum glazing is enhanced. A better energy-saving effects can be achieved using vacuum glazing replacing ordinary flat glass and insulating glass in energy-saving buildings. The average indoor temperature of energy-saving buildings using vacuum glazing for 7 d in winter is 3.91 K higher than that of using flat glass, and 2.25 K higher than that of using insulating glass.