Abstract: Through both analog simulation and theoretical analysis,the authors studied the features of overlying rocks structure and lower limit value of working resistance of hydraulic supports at fully mechanized working face under shallow buried and thick unconsolidated strata. The research results show that when mining thickness and thickness of bed rock strata at different working faces are same,while the thickness of unconsolidated strata over them is different,the overlying rock strata over the top coal caving working face under shallow buried and thick unconsolidated overburden all exist in the structure of “ combined cantilever-hinged rock beams-arch”. Based on the model of such overburden structure,the paper calculated analytic formula on the lower limit value of working resistance of hydraulic supports at top coal caving working face for ultra-thick coal seams under shallow buried and thick unconsolidated overburden. The field application results indicate that the analytic formulation for working resistance of hydraulic supports is properly calculated. The working resistance set with the formulation suit well to roof conditions of working faces.