The carbon dots were successfully prepared by hydrothermal reaction using citric acid as the carbon source firstly. And then the 7 - amino - 4 - methyl coumarin (AMC) was used to modify the carbon quantum dots in the EDC / NHS amide reaction system to a coumarin-modified carbon light stabilizer (AMC-CQDs). The optical properties and the application properties on the surface of the paper were studied, and the law of change on chromaticity of the paper was analyzed by the 1931-CIE chromaticity coordinates. The results revealed that the synthesized AMC-CQDs had uniform particle size (4.13nm), good water solubility and UV absorption which could realize the full coverage absorption in UV-light area. The maximum fluorescence emission wavelength of AMC-CQDs was 431nm, the fluorescence quantum yield was 38.7% and initial whiteness of the paper could be increased by 4.71 ISO%, which indicated that the compound was suitable for high yield pulp paper whitening. In addition, the results of chromaticity coordinates showed that the carbon light stabilizer had good performance on the physical whitening effect for the paper with chomaticity coordinates near the line y = 1.553x-0.184.