Abstract-Photovoltaic and photovoltaic heat technology can be coupled by nanofluid-based solar direct absorption thermal collector. It is an important means to improve the efficiency of comprehensive utilization of solar energy. Nanofluids optical theory plays an important role in the development of new photovoltaic-thermal experimental platform. In addition, study on optical characteristics of nanofluids is still in the initial stage. As a result, it is of great significance for the study of the law and mechanism of it. In this paper, the Rayleigh scattering model and the Mie scattering model are used to analyze the critical optical characteristics --transmittances of the nanofluids. Furthermore, the consistency between different theoretical models and experimental datum is studied by contrast verification between experiments and theory calculation. The conclusion shows that Mie scattering model performs better than Rayleigh scattering model and expresses a better applicability in the development of photovoltaic thermal experimental platform. This theoretical study on optical characteristics of nanofluids is expected to prompt on the application of nanotechnology in the field of solar energy. It is also expected to improve the efficiency of comprehensive utilization of solar energy.