According to the stage filling theory and particle interfering theory, a new parameter “q” was put forward. The “q” was come from other 3 parameters of Bailey method, which are CA, Fac and FAf, it is used to represent the internal composition of coarse aggregate. Focus on the tropical climate condition of Xishuangbanna which is located in Yunnan Province China, the gradation design and performance of asphalt mixture were in-depth studied. It is concluded that the “q” has an significant effect on the volumetric properties and pavement performances. When the “q”of AC-25 asphalt mixture ranges from2~5, the coarse aggregate is more easier to formed into skeleton, its resistance capability of high-temperature rutting and water damage are very good, and this kind of asphalt mixture can meet the challenge in tropical climate region.