This paper presents the development of a conductive composite film and the measurement of electromagnetic (EM) shielding effectiveness (SE) of the prepared film. A coaxial transmission-line technique based on ASTM D4935-99 Standard was used to measure the electromagnetic shielding effectiveness. A nickel nanofluid with an average particle size of 50 nm was prepared with a self-developed nanofluid synthesis system. By using a polymer blending method, carbon fiber and carbon fiber/nickel nanoparticles were blended with waterborne polyurethane (WPU) to prepare conductive composite films of 0.25 mm thick. Experimental results have shown that the electromagnetic shielding effectiveness value of the prepared conductive composite material can reach 26 dB within the range of 50 MHz ~ 1.5GHz.