This thesis, based on innovations and practices of methane drainage in multiseams of low permeability and complicated geology in Huainan mining district, systematically describes theories and key technologies of integrated pillarless coal production and methane extraction with "Y"  type ventilation system in multiseams of low permeability. Through analyses of deformation, fracturing and failure of rocks around goaf, methane movement and accumulation in and around the goaf are revealed, technologies to retain goaf edge roadways with innovative fill technologies are developed, and technological innovations in methane extraction are made with the retained goaf edge roadways and "Y"  type ventilation systems.