A　coupled　gas-solid　testing　system　was　developed　to　quantitatively　investigate　the　effects　of　gas　adsorption　on　the　strength,　volumetric　strain,　and　fracture　development　of　coal.　Uniaxial　loading　tests　were　conducted　on　coal　with　samples　that　had　adsorbed　helium　(He),　nitrogen　(N2),　methane　(CH4),　and　carbon　dioxide　(CO2)　gases.　Gas　adsorption　during　the　testing　process　was　graphed　using　MATLAB,　and　the　fractal　dimensions　of　the　fractures　in　coal　were　obtained.　Under　the　same　adsorption　pressure,　the　adsorption　capacity　and　degradation　rate　of　coal　were　found　to　decrease　in　the　following　order　for　the　four　gases:　CO2　＞　CH4　＞　N2　＞　He.　The　adsorption　of　CO2　had　a　salient　negative　affect　on　coal　strength,　while　the　effect　of　non-adsorptive　He　was　negligible.　The　peak　strength　decreased　by　48.27%　after　CO2　adsorption　at　a　pressure　of　2.0　MPa,　and　the　deterioration　rate　of　coal　strength　increased　logarithmically　under　adsorption　equilibrium　pressure.　The　fractal　dimension　and　density　of　coal　fractures　increased　with　adsorption　capacity.　The　degree　of　fracture　development　in　coal　with　adsorbed　CO2　at　a　gas　pressure　of　2.0　MPa　was　2.28-fold　that　of　coal　without　adsorbed　gas,　and　fish　scale-shaped　swelling　and　shedding　were　observed.　The　novel　findings　of　this　study　provided　a　scientific　basis　for　the　quantitative　evaluation　of　the　mechanical　properties　of　coal　with　adsorbed　gases.　©　2020