To explore the applications of carbon nano-materials in electromagnetic wave passive jamming field,the 8-12 GHz microwave attenuation performances of carbon nano-powder,carbon nanotubes,and carbon nanofibers were studied based on the static measuring method. The results indicate that the microwave attenuation performance of carbon nanofibers is better than that of carbon nanotubes and carbon nano-powder. The average microwave attenuation value per quality of carbon nanofibers with 60 nm diameter is between -2.84 dB and -4.27 dB, which is over 10 times of carbon nano-powder′s. It is concluded that the attenuation performance of carbon nanofibers with diameter of 60 nm is the best of these carbon nano-materials with different structures and sizes.