Abstract: For pressurizing of hydraulic support and water inrush disaster occurring during extending the upper extraction limit mining under unconsolidated confined aquifer, based on the key strata theory in rock stratum control, combined with structural characteristics of the overburden analysis, theoretical analysis and numerical simulation calculation is used to analyze overburden migration, underground pressure and support with surrounding rock relationship systematically during extending the upper extraction limit mining under unconsolidated confined aquifer, then the overburden breaking and migration characteristics under specific geological mining conditions are obtained, which reveals the mechanism of pressurizing of hydraulic support that the single key stratum breaking causing overburden overall composite breaking with the effect of high water pressure is essentially cause of pressurizing hydraulic support, and brings forward the prevention technology measures for pressurizing of hydraulic support on similar faces.