The reflection and thermal insulation performance of building reflective thermal insulation coatings will be impaired due to the influence of solar radiation, meteorological conditions and other uncontrollable external factors. However, the change in the performance of building reflective thermal insulation coatings in the time dimension is the key basic data to evaluate the energy-saving effect of buildings in a specific period, so it is of great practical and theoretical significance to clarify the impairment law of the performance of building reflective thermal insulation coatings in the time dimension. Architectural reflective thermal insulation coatings’ reflection and absorption characteristics are the intuitive embodiment of their properties. The change characteristics of coating properties in time scale can be correctly revealed by using hyperspectral technology to analyze the reflection and absorption characteristics of coatings quantitatively. In order to study and analyze the loss law of the performance of architectural reflective thermal insulation coatings on the time scale, hyperspectral technology is used as the main technical means in this study. Through the combination of indoor paint spectral determination experiment and paint sample external experiment to collect paint spectral data in different periods, and combined with spectral processing methods such as absorption peak depth and spectral analysis, the variation characteristics of spectral reflection and absorption characteristics of coatings in time dimension were quantitatively analyzed. In order to study and analyze the loss law of spectral reflectance of coatings under the influence of the external environment, the conclusions are as follows: (1) in the range of 350~2 250 nm, the spectral reflectivity of architectural reflective thermal insulation coatings decreases with the increase of time. The decreasing range of spectral reflectance increased from January to May but decreased from May to October, and the decreasing range of spectral reflectance in the visible region was significantly higher than that in the near-infrared region. (2) the absorption peak depth of building reflective thermal insulation coating decreases with the increase of time, and the decreasing range is within ［0, 0.163］. (3) the coating thickness has an important influence on the coating spectral reflectivity (coating performance) and its variation on the time scale, and the effect has strong stability, and the coating thickness has a strong influence on the weakening range of the coating spectral reflectivity. The consistency of the spectral reflectivity of architectural reflective thermal insulation coatings with single thickness changes with time and weakens with the increase.