During filling process of vacuum counter-pressure casting, the pressurizing velocity is one of the most important parameters, and it affects whole filling process of molten metal and the quality of castings, the pressurizing velocity must be reasonably controlled and chosen. Through analyzing the pressurizing velocity of vacuum counter-pressure casting filling process, the results show that pressurizing velocity is related with absolute temperature of down kettle gas, radius of rising tube, initial volume of down kettle, height from original position of molten metal to top of rising tube and gas flux. When other conditions are same during filling process of vacuum counter-pressure casting, pressurizing velocity is proportional to gas flux, and it is linear. Meanwhile, through experimental verification for relationship of pressurizing velocity with gas flux, their actual relationships and mathematical models are obtained, and correction coefficient is determined at the range from 0.95 to 0.98.