In this work, hollow fiber membrane contactor was used to theoretically study absorption carbon dioxide using water. Governing equations were solved by finite element method. The impact of temperature and velocity of liquid phase and velocity of gas phase on CO2 absorption flux has been investigated. Results showed that by increasing liquid phase velocity, CO2 absorption flux increases remarkably. Also, CO2 absorption flux increases only 6 % by increasing gas phase velocity from 0.02 to 0.06. Thus, liquid phase is the controller of mass transfer in gas absorption process. The results also showed that CO2 absorption flux decreases by increasing liquid phase temperature, due to the reduction of gas solubility in liquid phase, and outlet CO2 concentration of liquid phase decreases too. To validate of model’s results, the data of two experimental works have been used.