Carbon fiber paper was modified by adding carbon nanotubes to make it reach the demand of gas diffusion layer (GDL) by the process of impregnation with phenolic resin solution dispersed with carbon nanotubes, molding, and carbonization. The properties of modified carbon fiber paper, thickness, density, porosity, gas permeability, specific resistance and tensile strength, were characterized. The results indicate that surface treatment is helpful to disperse carbon nanotubes in phenolic resin. Phenolic resin is used to bond the carbon fibers, and carbon nanotube could reduce the specific resistance of the carbon fiber paper. When carbon nanotube content is 5 %, modified carbon fiber paper is prepared with thickness of 0.30 mm, density of 0.43 g/cm3, porosity of 77 %, gas permeability of 2400 mL•mm/(cm2•h•mmAq), specific resistance of 0.020 Ω•cm and tensile strength of 15 MPa, which basically qualifies for the application requirement.