In order to reveal the variation rule and mechanism of the voids in the mineral aggregate （VMA） of the same type of hot mix asphalt （HMA） at different gradations， the boundary particle size between coarse and fine aggregate and pass rate of the sieve holes x were used for the classification and analysis of the overall mineral aggregate to be graded. Based on the calculation formula of VMA and voids of coarse aggregate （VCA_mix） of HMA in which the proportion was determined， the physical relation between VMA and VCA_mix of the same type of HMA at different gradations was established through derivation. On this basis， the physical model of VMA was studied theoretically and verified by experiments. The results show that the increasing function of fine aggregate on VCA_mix in HMA and x are the two decisive factors affecting the VMA size. When x linearly increases VCA_mix， the VMA will either decrease in a convex curve or rise in a concave curve with the increase of x. When x exponentially increases VCA_mix， with the increasing of x the changing trends of VMA may be one of concave curve descending， convex curve descending， concave curve ascending， and complete concave curve similar to quadratic parabola with the opening upward.