In order to study the composite interference performance of carbon fiber with different particle diameters on infrared/millimeter wave, the attenuation rate of infrared and millimeter wave was tested on carbon fiber with different particle diameters under static test conditions using test samples, and the ones with the best attenuation effects for the two were selected. The far-infrared and 8 mm wave were selected as the attenuation objects. The smoke screen test box was used to dynamically test and analyze the carbon fiber with the best particle size characteristics to the infrared/millimeter wave of composite interference performance. The experimental results show that carbon fiber powder has a better attenuation effect on infrared, and the interference performance of chopped carbon fiber on millimeter wave is more significant. 800 mesh, 1.5 mm and 4 mm are the best particle sizes for carbon fiber attenuation of infrared/millimeter wave. The composite interference performance of each band is the best when the ratio is 22%, 4%, and 74%.