Abstract: In order to study the goaf gas ignition mechanism caused by the frictional effect between the broken rock blocks during the fracture and instability process of the hard sandstone roof,based on No. 32213(1) fully-mechanized coal mining face in Rujigou Mine as an engineering background,a theoretical analysis and in-door test method was applied to study the frictional flash temperature occurred in the shear sliding and instability process of the roof strata and the gas reaction process. The study showed that when the shear sliding and instability occurred in the overburden strata above the coal mining face,under the certain conditions,a high temperature friction surface would be formed within the shear sliding and instability zone and could ignite the gas within the zone and the surrounding area. When the friction speed between the hard sandstones was v6.0 m/s,the highest friction flash temperature would have a positive correlation to the quartz content of the sandstone. When the friction speed was higher,the heat density on the friction surface would be higher,the ignition energy would be higher and the gas would be more easily ignited.