Abstract: Capacitive deionization （CDI） is an emerging desalination technology that utilizes electric field forces to drive the adsorption of charged ions. Due to its low energy consumption and environmentally friendly nature, CDI exhibits significant potential for application in the field of water treatment. Electrode materials are a key component of CDI systems, and their electronic conductivity and interfacial wettability have a significant impact on desalination efficiency. Herein, short-cut pitch-based carbon fibers （PCF） with high electrical conductivity were used as raw materials. They are successively activated by KOH and nitric acid, which effectively increased the specific surface area and surface wettability of the prepared material （KN-PCF）. KN-PCF not only exhibits a specific surface area as high as 583.83 m²/g, but also shows a significant reduction in contact angle to 65° and a decrease in interfacial energy to 34.6 mN/m （a reduction of 60.1%）, while still maintaining excellent electrical conductivity （with a conductivity of approximately 13.7 S/cm）. Under a 1.4 V voltage applied in CDI, the KN-PCF electrode demonstrates a desalination capacity of 25.5 mg/g, an energy consumption of 0.77 Wh/g, and a desalination capacity retention rate of 96.7%. Density functional theory calculations reveal that the oxygen-containing functional groups on the KN-PCF surface effectively enhance the ion capture ability and improve the interfacial charge transfer efficiency through a dual mechanism of reducing the Na⁺ adsorption energy barrier and narrowing the HOMO-LUMO energy gap. In addition, the three-dimensional multi-physics field simulation designed through COMSOL software confirm that the uniformity of the electric field between the KN-PCF electrode and the electrolyte interface is significantly improved. This research provides theoretical and technical support for the high-value utilization of low-value pitch-based carbon fibers.