The work aims to improve the wet ability of carbon fiber applied in copper-water flat loop heat pipes and compare the advantages of different modified methods. The electroplate copper and flame spraying process metal powder were respectively used to form uniform copper plate and metal coating on the carbon fiber to modify the surface of carbon fiber. The treated surface morphology, improved wet ability and pumping of capillary wicks were characterized by high-speed camera, SEM and IR camera. The suction range was measured by IR image and mathematical model was established to quantitatively calculate the capillary pumping properties of carbon fiber after modification by two methods. As for the modified carbon fiber wicks by two methods, the internal porous structure was not damaged and the wet ability was improved significantly. The liquid drop could be absorbed into the fiber quickly after falling on the carbon fiber. The electroless plating was dense and flat and the flame spraying coating was free from crack and peeling off. The capillary pressures and permeability of the electroless plated carbon fiber capillary wicks were 3.2 kPa and 3′10-11 m2, while those for flame spraying metal coated carbon fiber were 2.94 kPa and 8.16′10-11 m2 respectively. These two methods both made the carbon fiber meet the requirements of flat loop heat pipe capillary wicks by modification. The treatment to the surface of carbon fiber by electro plating and flame spraying can improve the wettability of carbon fiber and then make the internal porous structure exhibit the capillary pumping ability for water. Carbon fiber can be used to replace the traditional sintering and metal mesh capillary wicks due to the flexible thickness not being limited by the evaporator size.