The effects of CDOC on the attenuation of close ultraviolet and blue light in Chaohu Lake and Longgan Lake were studied. Results revealed that the difference of soluble TC in two lakes was not significant, but CTOC in Chaohu Lake was larger than that of Longgan Lake. The absorb curve of CDOC with different sources was similar except for difference in quantity. In Chaohu Lake, there could be observed a peak between 355-400nm on the attenuation curve and K_d was larger, while in Longgan Lake, the attenuation curve was increased with decreasing wavelengths under 500 nm. The best relationship between K_d and CDOC was at 355 nm as the result of co-effect of suspended solids, Chlorophyll and CDOC.