Abstract: Aiming at the problem of air leakage control in overburden of mines transiting from open-pit to underground, the relationship between the gradation and thickness of overburden rock and air leakage is studied, and the method to determine the reasonable gradation and thickness of overburden is put forward.Based on the theory of air leakage in porous media, a physical similar experimental platform for ore drawing under overburden is built.Experiments on air leakage characteristics of overburden are carried out with 6 kinds of gradation to analyze the relationship between d₆₀/d₃₀, -0.5 mm fine particle content (t_{(-0.5 mm)}), -5 mm fine particle content (t_{(-5 mm)}) and air leakage respectively.Synergistic effect of porosity and thickness on air leakage is researched, and the reasonable gradation and thickness of overburden are determined.The results show that the relationship between porosity and grading index of overburden is monotonically decreasing, reducing porosity or increasing thickness can significantly reduce the air leakage of overburden, and air leakage is easier to be controlled when porosity is reduced to below 21.5%.The relationship model of air leakage with porosity and thickness is established, and then the reasonable gradation and thickness of the overburden without air leakage are obtained when the porosity is 20.0%-21.5%.The research provides theoretical guidance for the formation of overburden in mines transiting from open-pit to underground.