To increase electrosorption capacity and efficiency, there are many research concerning surface treatment of electrodes. In this study, fluorine functional group is introduced on a surface of activated carbon fiber (ACF), and it has a high negative charge due to its electronegativity. To introduce fluorine functional group on surface of ACF, ACF was modified by oxyfluorination using mixture gases of fluorine and oxygen with different partial pressure of F2: 0.1, 0.2, and 0.3 bar, and total pressure: 1 bar. The chemical composition changes of the untreated and oxyfluorinated ACFs were investigated using x-ray photoelectron spectroscopy. The CDI process was carried out at an electric potential of 0 ~ 1.2 V in 500 mg/L sodium chloride solution at 20 ml/min flow rate. The specific electrosorption capacity of optimized electrode (partial pressure of F2: 0.3 bar) was increased 116% compared to that of untreated electrode.