Abstract: Based on the existing national primary spectral radiance measurement facilities in the ultraviolet, visible and near-infrared wave bands, the measurement range of spectral radiance was extended to 2 µm~14 µm infrared band, which could be used for the metering calibration device of infrared spectral radiance and provided technical support for infrared spectral radiometric calibration in the fields of remote sensing earth observation, climate change, target recognition, material emissivity measurement and so on. The temperature uniformity and size-of-source effect of infrared spectral radiance measurement were studied. The temperature uniformity was improved by customizing the apertures or limiting the cavity position to be used in the system; the analysis and suppression of size-of-source effect were carried out by using optical simulation method, adopting limiting apertures in the system, simplifying the optical path and so on, which effectively decreased the uncertainty of the size-of-source effect. Next, the nonlinear effect and other parameters of the system will be studied, and the total uncertainty will be evaluated.