Abstract: In order not to have a mining face removing when a fully mechanized top coal caving mining face met a goaf of a former small mine and to improve the C oal mining recovery rate, a limited backfill reinforcement would be conducted in the goaf of the former small mine which was in the front of the coal mining face and thus the fully mechanized top coal caving mining face could be directly passed through the goaf.Therefore a key loading layer theory of an artificial roof was proposed and th e thickness over 5 m of the key layer was designed and calculated. Foaming cements with a compressive strength of 5.597 .43 MPa and a Ruimi backfill material with a C ompressive strength of 1.933 .95 MPa were tested and selected for the artificial roof material.The mechanics performances of the materials could meet the requirement s.A slicing grouting backfill method was applied and thus the backfill materials and solid coal could be fully bound to be integrated.The test results showed that with the backfill technology, within 25 days, the coal mining face had completed the 126 m mining in the goaf of the former small mine and about 1 million t coal was recovered.T he coal mining face successully realized the safety high efficient secondary mining directly passing through the goaf of the former small mine.