Rock quantitative remote sensing has gradually become the main means of mineral resources exploration and geological environment monitoring, and spectral unmixing is an important method for rock quantitative remote sensing. However, in practical application, because the satellite’s observation of the earth is influenced by topographic fluctuation, the observation has a certain angle, resulting in the variation of the measured emissivity spectrum. However, in the present study, the mineral endmember spectrum used for unmixing is obtained by vertical observation on the surface of the sample in the laboratory, ignoring the observation angle’s effect on the emissivity spectrum and reducing the unmixing spectral accuracy. Therefore, in this work, the observation angle is taken as the consideration factor to influence the unmixing spectral accuracy of rock. First, the common quartz, orthoclase and plagioclase surfaces are fabricated into general roughness, and a total of nine observation angles of 0°～77° are designed to observe the emissivity spectrum, and the effects on the thermal infrared spectral characteristics of the observation angles are analyzed. Secondly, using the mineral endmember with the observation angle of 13°~77°, the corresponding angle virtual rock spectrum is constructed, and the rock spectrum of 9 observation angles is unmixed with the mineral endmember of 0° spectrum, and the effect of the observation angle on the thermal infrared spectrum unmixing of rock is analyzed. The results show that: (1) in the range of 0°~20°, the observation angle has a weak effect on the spectrum, and the influence is significant from starting at 30°. Basic law: As the angle increases, the spectral absorption depth increases, but the situation at each band is different. The CF moves obviously to the short band direction after the observation angle is more than 50°. The absorption valley of RF is significantly deeper than 20°, and the valley bottom moves in short band direction. The emissivity of TF decreases significantly after the observation angles are greater than 40°. Therefore, the change of observation angle, will cause the obvious change of spectral characteristics. (2）In the range of 0°~20°, the effect of observation angle on spectral unmixing is not obvious, and the error of unmixing is less than 5%. When the observation angle is greater than 20°, the observation angle significantly affects spectral unmixing, the error of unmixing at 30°~77° is more than 5%, the average unmixing error reaches 17.2%, and the unmixing accuracy is low. This indicates that when the quantitative inversion of rock mineral components based on the spectral unmixing method is carried out, the influence of observation angle is considered, which is of great significance to improve the inversion accuracy and accurately determine the rock type.