The work aims to summarize law of influence of carbon fiber content and length on frequency dispersion characteristics of carbon fiber composite absorbing materials. Carbon fiber composite absorbing materials (CFCAM) of different length and content were prepared with carbon fiber (CF) with filler and water-based polyurethane resin (PR) as matrix basin. Microstructure and material structure of unmodified and modified CFCAM were characterized by means of scanning electron microscopy and X-ray diffraction analyzer. Dielectric constant of CFCAM was tested with vector network analyzer. The law of influence of CF length and content on frequency dispersion characteristics of CFCAM was summarized. ε of CFCAM first increased and then decreased as CF length increased. CFCAM with 3 mm CF not only had good frequency dispersion characteristics, but also had larger real (ε′) and imaginary (ε′′) part of dielectric constant. ε of CFCAM increased as the content of CF increased. ε′ of CFCAM was nearly 18 and imaginary part 9 at the CF mass fraction of 0.9wt.%, indicating that CFCAM had greater capability in storing energy, and had strong capability of electric loss on electromagnetic wave. 3 mm carbon fiber at the mass fraction of 0.9wt.% exhibits better frequency dispersion characteristic, hence it can be used to prepare radar absorbing materials of good absorbing property and wide frequency band.