Vacuum glazing is a very choice in building energy efficiency. Therefore, it is necessary to study on evacuating process of vacuum glazing. Based on fundamental pumping equation of vacuum technique and simplified the existing pumping system for vacuum glazing, a mathematical model, which is described evacuating process of vacuum glazing, is established. An exact mathematical solution is obtained by solving the model. According to the solution, an example from a practical evacuating system is solved and analyzed, and two conclusions are summed up as follows: First, the evacuating time needed for vacuum glazing is mainly depended on the flow conductance at vacuum glazing’s bleeding point; Secondly, the ultimate pressure of vacuum chamber should two orders of magnitude lower than the required pressure in the vacuum glazing. Above model, solution and conclusions have a certain guiding significance in the actual production of vacuum glazing.