Heat　injection　provides　a　feasible　approach　for　the　extremely　efficient　extraction　of　coalbed　gas.　Injecting　hot　steam　can　effectively　improve　the　pore　structure　of　coal　and　increase　the　permeability　of　coal.　To　observe　the　changes　in　the　pore　structure　of　coal　during　hot　steam　injection,　low　magnetic　field　nuclear　magnetic　resonance　technology　is　used　to　study　the　variations　in　the　pore　structure　of　coal　under　different　heat　injection　durations.　The　results　show　that　hot　steam　can　promote　the　formation,　growth,　and　expansion　of　coal　pore　fissures,　thereby　enhancing　the　gas　permeability　of　the　coal　seam.　At　the　same　time,　the　analysis　of　relevant　nuclear　magnetic　parameters　indicates　that　when　the　heat　injection　duration　is　15　minutes,　hot　steam　has　the　best　effect　on　coal　modification.　In　the　early　stage　of　hot　steam　injection,　hot　steam　stimulates　the　development　of　the　porous　structure.　In　the　middle　stage,　some　pore　structures　collapse　and　get　blocked　due　to　local　thermal　stress.　In　the　late　stage　of　hot　steam　injection,　hot　steam　accelerates　the　conversion　of　micropore　and　mesopore　structures　into　macropore　or　fissure　structures,　and　hot　steam　has　a　significant　modification　effect　on　coal.