At present, the highway construction of China is in the stage of rapid development. A variety of asphalt mixtures have been applied to a certain extent in the highway construction. However, the water stability of asphalt pavement is also a serious problem to the highway. This research studies the water stability of a new kind of asphalt mixture—Superpave by changing the water content in different condition. The following conclusion can be found in this paper. In the normal saturated condition, the maximum water content of Superpave asphalt mixture is 0.35%.And in the vacuum saturated condition, the maximum water content of Superpave asphalt mixture is 1.78%.The water of Superpave asphalt mixture takes nine days to drain completely in the normal saturated condition. But in the vacuum saturated condition, the time is more than two months. In different water content conditions, the splitting tensile strength of Superpave asphalt mixture is 0%> 100%> 25%> 75%> 50%.