Background disturbance is the main factor affecting the testing results of infrared radiation characteristics with non-full field of view(FOV). In this paper, according to Planck′s radiation law, the methods of measuring and calculating radiation characteristics of targets with non-full FOV were established with formula derivation and disturbance offset. On this basis, the infrared emissivities of aluminum plate and carbon nanotubes(MWCNTs)composite coatings were tested comparatively by using a SR-5000N spectroradiometer with both full FOV and non-full FOV. The results show that with non-full FOV, the infrared emissivities obtained by this method are in accord with the results measured with full FOV and can reflect the true spectral characteristics of the samples. This progress can effectively solve the FOV limitations to the radiation characteristics test of the target and greatly expand its application field.