An experimental apparatus that mimicked CO2 removal was established to evaluate a suitable solvent for CO2 removal under conditions approaching those of commercial reality. By this apparatus, various concentrations of methyldiethanolamine (MDEA) aqueous solutions and various ratios of methyldiethanolamine to piperazine (PZ) in activated MDEA solution were studied, and the results indicated that the optimum concentration of MDEA aqueous solution is 3.0 M and the optimum weight ratio of MDEA to PZ is 50/5.