Regard the mechanics model of key rock stratum in overlying strata as the single-span beam with semi-infinite length elastic foundation support. Based on elastic foundation beam theory, derive the analytic solution about inner force distribution of overlying strata. Then analyze the variation law of maximum value of bending moment and its location of overlying strata followed by beam space and relative rigidity. Through the research and analysis, the relationship between the elasticity of elastic foundation and the stress field of digging area is elaborated.