At present, AC, a major gradation type of asphalt mixture, is widely used in highway construction in China. Due to internal large porosity, the water of road surface draining quickly, OGFC pavement is also widely used. However, water is easier flow into OGFC asphalt pavement than ordinary asphalt pavement. So the water stability of OGFC asphalt pavement is particular important. We get the following conclusion by the test of residual water and water stability based on the two gradations asphalt mixture of AC and OGFC. Residual water stays in AC asphalt mixture for about one week.While the residual water stays in OGFC asphalt mixture for more than three months. When the residual water is 50% in AC, the water stability is the worst. When the residual water is 75% in OGFC, the water stability is the worst.