The spectral radiation in the light source is an essential cause of color damage, such as fading and discoloration of painted cultural relics. However, the spectral power distribution of different light sources is different, and the absorption and reflection characteristics of different materials to the radiation energy of each waveband are different, which leads to a great difference in the degree of damage caused to colorful cultural relics under the same exposure. Especially with the extensive application of LED with flexible spectral composition in cultural relic lighting, how to evaluate the lighting damage degree of the light source is the critical problem that needs to be solved. In this study, a 1440 hours experiment was used to irradiate 17 kinds of typical pigments of polychrome cultural relics with 10 kinds of narrow band spectrum under the constant temperature and humidity. By measuring the CIE L*a*b*and calculating the color difference of pigments under different light sources every 240 hours, the curve of color difference changing with exposure was drawn. Based on the curve analysis, the change law and color damage response function of pigments to different wavebands is obtained, and the formula to evaluate the damage degree of lighting source on polychrome cultural relics is established. The results show that: firstly, no matter under any kind of narrow band spectrum, the average color difference of pigments increases with the increase of exposure, but the increased range is smaller and smaller; Secondly, under the same exposure, the shorter the wavelength, the greater the damage to the pigments. The influence ratio of different peak wavelengths to the pigments is 447 nm∶475 nm∶500 nm∶519 nm∶555 nm∶595 nm∶624 nm∶635 nm∶658 nm∶733 nm=1.000∶1.096∶0.816∶0.921∶0.853∶0.777∶0.814∶0.796∶0.706∶0.674; thirdly, the formula for damage evaluation of the light source based on the difference of spectrumis, D=∫780380S(λ)〈0.468exp｛-［(λ-462.9)/17.75］2｝+0.627 9exp｛-［(λ-535.1)/12.13］2｝+0.813 5exp｛-［(λ-527.7)/463］2｝〉dλ, When the relative spectral power distribution function S(λ) of any light source is measured by the spectrometer, the color damage value D of the light source to be measured can be calculated by substituting the measured data into the formula.