In order to reduce the cost of ionie liquids (lLs) and imprve their carbon capture capacity, four kinds of imidazolium-based anion-functionalized ionic liquids were prepared with ethyl tributyl phosphonium ([P4442]+) as cation and imidazole ([Im]-), 4-methylimidazole ([4-MeIm]-), 4-bromimidazole ([4-BrIm]-) or 4-nitroimidazole ([4-NO2Im]-) as anions. The density, viscosity and carbon capture properties of ILs were measured. The effects of substituents on the 4th position of anions on carbon capture properties of ILs were investigated. The carbon capture mechanism of [P4442][Im] was studied by13C NMR and FT-IR. The results showed that the order of carbon capture capacity of ILs at 30 °C and 0.1 MPa was as follows: [P4442][Im] > [P4442][4-MeIm] > [P4442][4-BrIm] > [P4442][4-NO2Im], indicating that the weak electron-pushing effect of methyl group could not improve the carbon capture performance, while the electron-withdrawing effect of bromine or nitro group could significantly inhibit carbon capture capacity by dispersing negative charge density of anions. The substituents on 4th position increased the density and viscosity of ILs. The saturated CO2 absorption of [P4442][Im] was as high as 1.0 mol CO2/mol IL. [Im]-could chemically interact with CO2, thereby enhancing the carbon capture ability.