The　effect　of　organic　cation　doping　with　aziridinium　(Az+)　on　the　material　properties　of　CsPbI3　was　investigated　by　applying　first-principles　calculations.　The　results　showed　that　the　phase　stability　is　greatly　improved　by　incorporating　the　organic　cation　Az+　at　the　A　site　of　CsPbI3.　However,　the　band　gap　of　CsPbI3　is　further　enlarged　from　1.76　to　2.27　eV　when　12.5%　of　Az　doping　is　used.　The　optical　absorption　coefficient　of　Cs0.875Az0.125PbI3　is　also　decreased　in　the　visible　light　region.　The　reasons　of　the　improved　phase　stability　and　the　enlargement　of　band　gap　arising　from　the　organic　cation　doping　are　revealed.　Our　calculated　results　can　provide　theoretical　guidance　for　improving　the　phase　stability　of　halide　perovskites.　©　2019　American　Chemical　Society.