In　this　work,　a　rational　ionic　liquid　(IL)　design　and　screening　strategy,　including　vapor-liquid　equilibrium-based　absorption-selectivity-desorption　index,　simultaneous　and　step-wise　separations,　thermodynamic　and　physical　property　constraints,　and　process　simulation,　is　established　to　remove　SO2　and　CO2　from　flue　gas.　Based　on　the　UNIFAC　method,　the　vapor-liquid　equilibrium　composition　of　flue　gas　is　considered　to　calculate　the　absorptivity,　selectivity,　and　desorptivity　of　two　separation　processes.　Through　benchmark　solvents,　melting　points,　and　viscosity　constraints,　five　optimal　ILs　are　obtained.　Finally,　optimal　ILs　with　reported　ILs　1-ethyl-3-methylimidazolium　tetracyanoborate　[EMIM][TCB]　and　1-ethyl-3-methylimidazolium　tetrafluoroborate　[EMIM][BF4]　are　introduced　to　Aspen　Plus.　In　light　of　solvent　requirements　and　energy　consumption　analysis,　1-(2-hydroxyethyl)-imidazolium　bis(trifluoromethylsulfonyl)amide　[C2OHIM][Tf2N]　and　1-ethylpyridinium　dicyanamide　[C-2PY]-[DCA]　are　selected　as　the　best　IL　absorbents,　the　processes　of　which　save　55.71　and　31.25%　solvent　and　70.73　and　24.52%　energy　compared　to　[EMIM][TCB]　and　[EMIM][BF4],　respectively.　Furthermore,　stepwise　separation　saves　at　least　50%　energy　compared　to　simultaneous　separation.