Abstract: Waterproof coal pillar reasonable design is a fundamental parameter of coal extraction devising under extremely thick unconsolidated strata. By analysis of Quaternary extremely thick unconsolidated strata geological characteristics, the influence of thickness and structural distribution properties of a quifer and aquifuge under extremely thick unconsolidated strata on water inrush during coal extraction was revealed, the waterproof coal pillar design computing model and theory under extremely thick unconsolidated strata were established, nonlinear computational method under extremely thick unconsolidated strata was put forward, and the waterproof coal pillar design height of number 8 coal seam in Donghuantuo coal mine is 65.62 m. According to fluid-mechanical interaction theory, using FLAC^3D numerical simulation calculation software, further simulation on overlying strata deformation and failure law of number 8 coal seam exploitation in Donghuantuo coal mine was carried out.Distribution law of coal seam roof rock caving zone, aquiferous crevice zone and curve subsidence zone was revealed, waterproof coal pillar design height and related engineering technique parameters were acquired, the reliability of nonlinear design method and computational model of waterproof coal pillar design under extremely thick unconsolidated strata is validated, and the feasible approaches to waterproof coal pillar reasonable design under extremely thick unconsolidated strata were explored.