Structural　effects　on　various　imidazolium?based　ionic　liquids　(ILs)　(i.e.,　[C][A],　[C]　=　[EMIM]+,　[BMIM]+,　and　[OMIM]+;　[A]　=　[BF4]?,　[PF6]?,　and　[Tf2N]?)　suitability　as　drying　agents　for　gas　dehydration　processes　are　explored　from　thermodynamic　and　dynamic　insights　by　quantum　chemistry　(QC)　calculations　and　molecular　dynamics　(MD)　simulations.　It　is　found　that　[EMIM][BF4]　is　regarded　as　the　most　promising　drying　agent　because　it　exhibits　the　lowest　Henry?s　law　constant　and　highest　diffusion　coefficient　of　H2O　among　all　ILs.　The　microscopic　mechanism　at　molecular　level　is　revealed　based　on　QC　calculations　and　MD　simulations,　and　the　results　demonstrate　that　the　IL　(i.e.,　[EMIM][BF4])　simultaneously　with　the　smallest　cation　and　anion　size　corresponds　to　both　the　strongest　hydrogen　bond　(HB)　interaction　of　H2O?anion　and　the　strongest　HB　together　with　van　der　Waals　interactions　of　H2O?cation.　This　work　provides　a　valuable　guidance　from　viewpoint　of　thermodynamics　and　dynamics　for　developing　and　screening　novel　ILs　for　gas　dehydration.