Aimed at the low mining efficiency in deep multi-seams because of high crustalstress,high gas content,low permeability,the compound “three soft” roof and the trouble-somesafety situation encountered in deep level coal exploitation,proposed a new idea ofgob-side retaining without a coal-pillar and Y-style ventilation in the first-mined key pressure-relieved coal seam and a new method of coal mining and gas extraction.The followingwere discovered:the dynamic evolution law of the crannies in the roof is influenced bymining,the formative rule of “the vertical cranny-abundant area” along the gob-side,thedistribution of air pressure field in the gob,and the flowing rule of pressure-relieved gas ina Y-style ventilation system.The study also established a theoretic basis for a new miningmethod of coal mining and gas extraction which is used to extract the pressure-relievedgas by roadway retaining boreholes instead of roadway boreholes.Studied and resolvedmany difficult key problems,such as,fast roadway retaining at the gob-side without a coalpillar,Y-style ventilation and extraction of pressure-relieved gas by roadway retainingboreholes,and so on.The study innovated and integrated a whole set of technical systemsfor coal and pressure relief gas extraction.The method of the pressure-relieved gasextraction by roadway retaining had been successfully applied in 6 typical working faces inthe Huainan and Huaibei mining areas.The research can provide a scientific and reliabletechnical support and a demonstration for coal mining and gas extraction in gaseous deepmulti-seams with low permeability. Aimed at the low mining efficiency in deep multi-seams because of high crustalstress, high gas content, low permeability, the compound “three soft ” roof and the trouble-somesafety situation encountered in deep level coal exploitation, proposed a new idea ofgob -side retaining without a coal-pillar and Y-style ventilation in the first-mined key pressure-relieved coal seam and a new method of coal mining and gas extraction.The following were discovered: the dynamic evolution law of the crannies in the roof is influenced bymining, the formative rule of “the vertical cranny-abundant area ” along the gob-side, the distribution of air pressure field in the gob, and the flowing rule of pressure-relieved gas ina Y-style ventilation system. also established a theoretic basis for a new mining method of coal mining and gas extraction which is used to extract the pressure-relieved gas by roadway retaining boreholes instead of roadway boreholes. Studied and resolvedmany difficult key problems, such as as , fast roadway retaining at the gob-side without a coalpillar, Y-style ventilation and extraction of pressure-relieved gas by roadway retaining coreholes, and so on. The study innovated and integrated a whole set of technical systems for coal and pressure relief gas extraction. The method of the pressure-relieved gasextraction by roadway retaining had been successfully applied in 6 typical working faces inthe Huainan and Huaibei mining areas. The research can provide a scientific and reliable technical support and a demonstration for coal mining and gas extraction in gaseous deepmulti-seams with low permeability.