Aiming at the actual demand, the gas flow characteristics of butterfly vacuum control valves are investigated in this paper. Classification and characteristic of vacuum control valves are discussed in detail. The geometric and mathematic models for two kinds of butterfly vacuum control valves, with seal and without seal, are respectively built. The gas flows through the valve at different opening angles are simulated under different pressure by means of the Fluent software. The flow percentage function and adjustment sensitivity are introduced and formulated to describe the flow regulating characteristic of control valves. The flow conductance coefficient and flow loss coefficient are defined and formulated to describe the resistance characteristic of control valves. The dates and curves of some simulating examples are given and discussed.