Coal is the most important energy source in China. In mining, coal cutting, transportation, washing, processing, and cleaning coal storage, it is necessary to know the composition and content of coal and the degree of mixed gangue in time of determining, master and monitor the quality of coal. At present, based on visible light to the near-infrared emission spectrum of coal, in situ testing technology has become a research hotspot, and the granularity is one of the important factors affecting spectral characteristics to carry out the granularity to study the influence of the different spectral reflectance characteristics of coal, to understand the spectral characteristics of coal deeply. Coal spectrum recognition accuracy is of great significance. For this purpose, this article selects the main coal enrichment region (including Inner Mongolia Wuhai, Xinjiang Hami, Shanxi Yangquan) of lignite, bituminous coal, and anthracite as the research object by using an SVC HR-1024 spectrometer with different granularity coal- near-infrared spectrum of visible light sample test, analyzes the particle degree of the influence law of spectral reflectance of coal samples, and the difference of the influence of granularity on the spectrum of different coal. On this basis, the physical mechanism behind the experimental phenomenon is analyzed and discussed. The results show that the emission spectrum characteristics of coals with different metamorphic degrees are similar. In other words, the reflectance is the low invisible band and decreases slowly with the increase of wavelength, while it rises rapidly in the near-infrared band. When the granularity of the coal sample is greater than 0.10 mm, the granularity has little influence on the spectral characteristics, and the change law of the reflection spectrum with granularity is not obvious. When the granularity is less than 0.10 mm, the influence of granularity on the spectrum of the coal sample increases. In addition, the influence is mainly reflected in the slope of the reflectance spectral curve of the near-infrared band. The smaller the granularity is, the more significant the reflectivity increment is and the larger the slope of the spectral curve is. A granularity of 0.10 mm can be used as the sensitive limit of granularity’s influence on the coal’s spectral characteristics. The spectral curves of different coal types are affected by particle size to different extents, and the impact on lignite is the largest, followed by bituminous coal, and the least impact on anthracite. It can be seen that when using the reflectance spectrum to analyze coal quality and identify coal species, the effect of selecting a powder sample with granularity of less than 0.10 mm is better than that of a large particle or lump sample.