Phytoplankton absorption and chlorophyll-specific absorption coefficients were analyzed,and the causes were discussed by selecting four different trophic level lakes including Lake Taihu,Lake Tianmu and Lake Bositeng.According to trophic level index using chlorophyll-a(Chl.a),total nitrogen,total phosphorus and secchi disc,Lake Taihu includes hyper and medium eutrophication zones.Meanwhile,Lake Tianmu and Lake Bositeng are light eutrophic and mesotrophic,respectively.Phytoplankton absorption coefficients at 440 nm (a_ph (440)) are 1.02±0.51 and 0.69±0.40 for hyper and medium eutrophication in Lake Taihu,0.78±0.24 in Lake Tianmu,and 0.20±0.04 m^-1 in Lake Bositeng,respectively.Correspondingly,a_ph (675) are 0.59±0.32,0.38±0.23,0.41±0.13 and 0.08±0.02 m^-1,respectively.Statistics test shows that phytoplankton absorption of hyper and medium eutrophic Lake Taihu,in addition to light eutrophication Lake Tianmu,is significantly higher than that in mesotrophic Lake Bositeng.Chlorophyll-specific absorption coefficients at 440 nm (a_ph^* (440)) are 0.013±0.006,0.012±0.004, 0.038±0.008 and 0.051±0.013 m²/mgChl.a,respectively.Statistics test shows that a_ph^* (440) of Lake Taihu is much lower than that of Lake Tianmu,and a_ph^* (440) of Lake Tianmu is significantly less than that of Lake Bositeng.The order of the spectral absorption coefficient is as follows: Lake Taihu TⅠ > Lake Tianmu > Lake Taihu TⅡ > Lake Bositeng,showing that phytoplankton absorption coefficients generally increase with trophic levels,but Lake Taihu TⅡ is lower than Lake Tianmu partly due to the high concentration of non-algae suspended matter.In contrast,chlorophyll-specific absorption coefficients decrease with enhanced trophic levels.Phytoplankton absorption coefficients generally increase with trophic levels due to the increase of biomass caused by high nutrient concentration.However,the decrease of chlorophyll-specific absorption coefficients with enhanced trophic level may be attributed to pigment package.