The reduced graphene oxide/nano-copper composites were prepared by using in-situ reduction method and characterized. The complex refractive index of the composites in middle and far infrared band were measured, and its absorption coefficient and normal spectral emissivity in the atmospheric window were calculated and verified by experiment, along with the analysis of its absorption and radiance performance in middle and far infrared. The results show that nano-coppers are adsorbed on the surface of reduced graphene oxide, and its size almost concentrate in 15~25 nm. Due to the different sizes of nano-copper, and reduced graphene oxide together with its surface defects and functional groups, the composites have a strong absorption performance in 8~9.2 μm, 6~6.5 μm, 2~3 μm. Its normal spectral emissivity in 3~5 μm is within 0.65~0.68, but it has a minimum value of 0.53 in 8~9.5 μm, and then stabilize at about 0.58. Their total normal emissivity is 0.66 and 0.59 respectively, which are consistent with the experiment. The composites can be used for infrared absorption, extinction materials and stealthy coatings.