Abstract: According to the actual condition that hydraulic supports are pushed down not to extensible in 40112 fully mechanized caving face of Shaanxi Bingchang Dafosi Mining Co., Ltd, it analyzes the reasons for causing hydraulic supports pushed down not to extensible from mining pressure, equipment model, working face project quality, mining technology and so on. It puts forward the targeted treatment methods and prevention measures, which has certain reference significance for eliminating similar accidents.