Separation and capture of carbon dioxide from the flue gas of power plants in order to reduce environmental damages has always been of interest to researchers. In this study, aqueous solution of methylamine was used as an absorbent for CO2 capture. In order to study this reaction, Density Functional Theory (DFT) was employed at the level of B3LYP/6-311++G(d,p) by using the conductor-like polarizable continuum model (CPCM). Two possible reaction products were studied: carbamate ion and bicarbonate ion. The estimation of the thermodynamic parameters indicated that the reaction of bicarbonate ion forming is not thermodynamically feasible at room temperature. However, the reaction of carbamate ion formation is exothermic (ΔH= -12.4 kcal mol-1) and exergonic (ΔG= -1.48 kcal mol-1). Also, various atomic radii were employed to build up the solute cavity within CPCM model and the effects of the solute cavity on the thermodynamic properties of the reaction were studied.