Aim at the phenomenon of by mining on the condition of shallow coal seams, article bases on locale observation, and gives the expression on different the ratio of rock and loading(RRL), the ratio of rock and mining(RRM) and overturn destruction forms by analyzing, it in virtue of determining key strata and key strata flexibility calculation and utmost subsidence on the condition of destruction, and expatiates the characteristic of η on the condition of shallow coal seams, and makes it divide into subsection function. Study indicate: if subsection function, η is applied, then using it to forecast the quantity of surface subsidence that will be more approach to fact, which can syllabify explain phenomenon of sidestep subsidence on surface, and has definite meaning to coach locale.