To enhance the adsorption capacity of activated carbon fibers (ACF) towards heavy metals, the surface modification of ACF was conducted and the physical and chemical characteristics were analyzed. Additionally, the competitive adsorption of Pb(Ⅱ), Cu(Ⅱ) and Co(Ⅱ) from liquid solution on the modified ACF were evaluated. It was found that both the modified and unmodified ACF had large specific surface areas and pore volumes. Compared with the unmodified ACF, the crystallinity of Fe and HNO₃ modified ACF showed a trend of decrease, and the Fe modified ACF appeared on obvious Fe characteristic diffraction peak. The rate of heavy metal ions adsorption onto ACF were so fast that the adsorption equilibrium achieved at about 60 minutes, and the adsorption equilibrium time increased after the Fe and HNO₃ modification. The removal of Pb(Ⅱ), Cu(Ⅱ) and Co(Ⅱ) were influenced significantly by the initial pH. The adsorption affinity to the three heavy metals was in the order of Pb > Cu > Co for all types of ACF. With the increase of initial concentration, the adsorption amount of Pb(Ⅱ) and Cu(Ⅱ) increased, while the adsorption amount of Co (Ⅱ) increased firstly and then decreased. The Langmuir and Freundlich models could well describe the competitive adsorption process of Pb (Ⅱ) and Cu (Ⅱ), but not effectively simulate the adsorption process of Co (Ⅱ).