An experimental process of separating a mixed gas of NH3/CO2 = 2 (mole ratio) contains a first section, which is a two-step series bubble absorber for selective absorption of NH3 under 80140 m/s inlet velocity, and a second section, which is a free NH3 recovery of the obtained aqueous solution followed by desorption of the solution. In the two-step series absorber, the total absorptivity of NH3 reaches 96.7% and the total absorptivity Of CO2 is only 33.1%, so the exit content of CO2 for the second step absorber reaches 90.9% (by mole). Free NH3 of the solution is recovered to liquid NH3 with a purity of 99.9% under 1.7-1.9 MPa, and the remaining solution is then desorbed to NH3 and CO2, which is returned to the front first absorber for continuing separation. Then the discharged liquid contained 0.014% NH3 and 0.006% CO2; it can be returned to the absorption system to be used. From this experimental condition, the heat consumption for the separating process is estimated at 3.4 kg of steam of 1 MPa/kg of NH3.