Based　on　the　modified　programmed　temperature-raising　system,　cyclic　thermal　stimulation　with　different　temperature　gradients　was　carried　out　for　lignite,　bituminous　and　anthracite　coal,　and　each　group　of　coal　samples　after　thermal　stimulation　cycle　was　subjected　to　nuclear　magnetic　resonance　(NMR)　testing.　The　NMR　T1-T2　spectra　and　the　fractal　dimensions　of　coals　in　different　ranks　during　thermal　simulation　quantitatively　described　the　dynamic　evolution　of　the　pore　fluid　storage　space　of　coals.　The　variation　of　T2　distribution　and　pore　throat　were　used　to　reflect　the　pore　development　process　of　coals.　The　results　shows　that　the　pores　and　pore　throat　of　lignite　developed　the　best　among　the　three　coal　ranks　and　the　structure　of　the　pore　is　complete　after　the　cyclic　thermal　simulation;　the　T1-T2　signal　peaks　increased　from　17.05　at　30　degrees　C　to　163.00　at　180　degrees　C;　the　seepage　of　lignite　increased　from　6.54　%　to　12.43　%;　total　pore　fractal　dimension　DT　has　a　decreasing　trend,　indicating　reduced　inhomogeneity　of　pores.　This　indicates　that　the　cyclic　thermal　stimulation　treatment　can　promote　the　growth　of　seepage　pores　to　a　greater　extent,　improve　the　seepage　space,　and　enhance　the　connectivity　of　the　pores　in　the　coal　samples.