Abstract: The determination of a reasonable cover layer thickness has always been a puzzle for mines that are transitioning from open pit to underground mining.Starting from the function of the cover layer, and based on the analysis of the factors influencing the cover layer thickness, the relationship of the cover layer thickness with the mining technology, and with the mine water prevention and drainage were discussed, the model for the relationship between the height of drawing ellipsoid and that of loosening body was deduced and test was conducted to measure the leakage factor of the cover layer formed by granular rock, hereby providing a theoretical guidance to the determination of the optimized cover layer thickness for the mines transitioning from open pit to underground mining.

Key words: Transition from open pit to underground mining, Cover layer thickness, Drawing ellipsoid, Granular leakage