Absorption rate of CO2 into aqueous solution of N-methyldiethanolamine (MDEA) blended with di-ethanolamine (DEA) and piperazine (PZ) was studied and a kinetic model was established. It is shown thathomogeneous activation mechanism could explain this absorption process. The absorption rate coefficients of car-bon dioxide into MDEA aqueous solution blended with DEA, PZ or DEA+PZ were compared with each other. Theresults demonstrated that the different activation effect of DEA, PZ and DEA+PZ on the carbon dioxide absorptioncomes from the difference in CO2 combination rate, transport of PZ and DEA to MDEA and the regeneration rateof PZ and DEA.