The　adsorption　and　diffusion　of　gases　in　porous　media　are　fundamental　phenomena　that　find　widespread　application　in　the　energy　and　chemical　industries.　In　this　study,　we　used　Grand　Canonical　Monte　Carlo　and　molecular　dynamics　simulation　methods　to　evaluate　the　adsorption　and　diffusion　properties　of　CO2　and　H2　in　the　calcite　silt-like　pores.　We　report　the　influence　of　pressure,　pore　size,　and　temperature　on　adsorption　isotherms　(i.e.,　total,　absolute,　and　excess)　and　diffusion　coefficients　(i.e.,　self-diffusion,　Fick　transport　diffusion,　and　Maxwell-Stefan　diffusion).　The　results　reveal　a　greater　CO2　adsorption　capacity　compared　to　H2　and　the　easy　absorption　of　the　oxygen　atoms　of　CO2　onto　the　surface　of　calcite.　The　adsorption　capacities　of　CO2　and　H2　increased　together　with　the　pressure,　and　the　pore　size　had　little　effect　on　the　absolute　adsorption　capacity　and　density　distribution　of　the　pure　compounds.　The　interaction　energy　between　calcite　and　CO2/H2　showed　that　the　calcite　had　greater　affinity　for　CO2　than　for　H2.　The　CO2　diffusion　coefficients　were　smaller　than　those　of　H2.　The　diffusion　coefficients　of　CO2　and　the　mutual　diffusion　coefficients　of　the　gas　mixture　increased　with　increasing　pressure　before　stabilizing.　In　contrast,　the　diffusion　coefficients　of　H2　decreased　with　an　increase　in　pressure.　©　2021　Elsevier　B.V.