1-allyl-3-methylimidazolium formate ([Amim][HCOO]) exhibited higher solubility for various polysaccharides because of the strong hydrogen bond ability. In this work, the density and viscosity of [Amim][HCOO] were measured at different temperatures, the CO2 and CH4 solubilities in [Amim][HCOO] were determined at temperatures from 298.15 to 333.15 K and at pressures up to 2 MPa. The density and viscosity of [Amim][HCOO] were fitted by semi-empirical equations, and the experimental gas solubility was represented by thermodynamic model. The energy consumption for CO2 separation was calculated and compared with the conventional ILs.