Abstract: To research the failure features of overlying strata and safety mining of fully-mechanized caving mining in nearly thick unconsolidated formation, firstly, we analyzed the features of engineering geology and hydrogeology of layers in study area, and studied the failure features of overlying strata with different thickness of bedrock by UDEC 4.0. The results indicate that coal mining in this area can be with the sand-proof coal pillars because of the weaker watery at the bottom of loose aquifer and poor supply condition; under the conditions of fully-mechanized caving mining, with the bedrock thickness changing, the deformation and failure features of overlying strata have significant differences; when the caving-height ratio is 3.55, the thickness of bedrock is less than 40.4 m, the support crushing and water inrush accidents will be occurred easily in this situation.