Colorimetric studies of different light path lengths from a new perspective of UV-Vis spectroscopy. The corrected ultraviolet-visible light spectrum was used to calculate the color of flame-fusion synthetic ruby, and the influence of light path length and standard light source on the color of flame-fusion synthetic ruby was studied. The results show that the L*, C*, h° under the A light source are higher than those under the D65 light source. In the ultraviolet-visible light spectrum, the strong absorption band of Cr3+ at 545nm is the main cause of the color of the ruby. As the length of the light path increases, the absorption peak area at 545nm also increases, the lightness L* decreases, and the hue angle h° increases. The chroma C* first increases as the length of the light path increases, and then begins to decrease under the influence of the continuous decrease in lightness. The color difference ΔE*ab reaches the maximum when the light path length is around 10mm, and the standard light source has the greatest influence on the color difference ΔE*ab. As the length of the light path continues to increase, the influence of the standard light source on the color difference\(\)ΔE*ab decreases.