Two-film gas transfer theory was applied to analyze carbon dioxide absorption across the gas-liquid interface with diethanolamine (DEA) solution. Mathematical models were developed to describe the dependence of CO2 transfer rate on pH value and the degree of rate enhancement due to chemical reactions with DEA. Various concentrations of carbonic species in the bulk liquid [i.e., DCDt(RNHCOO-), DCDt(HCO3-) and DCDt(CO32-)] in time were considered to affect total mass transfer rate. Various technological parameters, such as DEA concentration, CO2 flow rate and ratio of absorption blends were controlled. The results show that CO2 transfer rate is mainly contributed by CO32- and HCO3-, but the transfer rate of RNHCOO- is not significant. The CO2 transfer rate is promoted by the increase of DEA concentration, but the effect will decrease after pH value falls to 8.2. When CO2 flow rate increases, the transfer rate will increase until 70 mL/min. Blend solution is better than single DEA solution in CO2 absorption, but the effect of the ratio of blend is not significant on contribution ratio of carbonic species to total mass transfer rate.