Natural　gas　dehydration　is　a　critical　process　in　natural　gas　extraction　and　transportation,　and　the　membrane　separation　method　is　the　most　suitable　technology　for　gas　dehydration.　In　this　paper,　based　on　molecular　dynamics　theory,　we　investigate　the　performance　of　a　metal-organic　composite　membrane　(ZIF-90　membrane)　in　natural　gas　dehydration.　The　paper　elucidates　the　adsorption,　diffusion,　permeation,　and　separation　mechanisms　of　water　and　methane　with　the　ZIF-90　membrane,　and　clarifies　the　influence　of　temperature　on　gas　separation.　The　results　show　that　(1)　the　diffusion　energy　barrier　and　pore　size　are　the　primary　factors　in　achieving　the　separation　of　water　and　methane.　The　diffusion　energy　barriers　for　the　two　molecules　(CH4　and　H2O)　are　Delta　E(CH4)　=　155.5　meV　and　Delta　E(H2O)　=　50.1　meV,　respectively.　(2)　The　ZIF-90　is　more　selective　of　H2O,　which　is　mainly　due　to　the　strong　interaction　between　the　H2O　molecule　and　the　polar　functional　groups　(such　as　aldehyde　groups)　within　the　ZIF-90.　(3)　A　higher　temperature　accelerates　the　gas　separation　process.　The　higher　the　temperature　is,　the　faster　the　separation　process　is.　(4)　The　pore　radius　is　identified　as　the　intrinsic　mechanism　enabling　the　separation　of　water　and　methane　in　ZIF-90　membranes.