Solar spectroradiometer, as a special instrument for measuring solar spectral radiation, accurate and complete characterization of whose spectral properties is very important for the wide spectral range and the large dynamic range of solar radiation. The purpose of this paper is to provide explicit theory evidence and test method for the development and validation of solar spectroradiometer, and also to give clear and accurate mechanism models and characteristic indicator models for design and evaluation of the spectroradiometer system. Therefore, this paper focuses on the derivation and modeling process from signal transfer model to performance indicator model of spectroradiometer system. Spectral line spread function model, which is a convolution of series kernel functions, could synthetically indicate the influence of each component of the instrument on the system, and it’s easy to obtain by measuring a narrow band spectral line light source, and spectral line spread function matrix can clearly and completely show the instrument characteristics in details of the spectroradiometer. On the basis of spectral line spread function, the key geometric features are extracted further. Defined by simple algorithms, three characteristic indicators such as the full width at half maximum (FWHM), out-of-band rejection and out-of-band radiation are obtained. They can be used to quantitatively characterize the performance of the instrument for spectrometry, and are very effective characteristic indicator models for evaluating the performance of spectroradiometer system.