Cell number, cell size, chlorophyll-a (Chl.a) concentration, absorption and specific absorption coefficients of Microcystis aeruginosa and Scenedesmus obliqnus were determined in the different culture times at three different irradiation intensities. Oneway analysis of variance showed that irradiation intensity had great significant effects on cell number, Chl.a concentration and phytoplankton absorption coefficients at 440 nm a_ph (440), 675 nm a_ph (675) in the entire experimental period. The largest values of these parameters were recorded in the light condition with 50 μmol/(m²·s). Phytoplankton needs optimal growth irradiation intensity because over-low or high light density could have negative effects on the growth rate of phytoplankton. Correlation analysis showed that there were significant positive correlations between a_ph (440), a_ph (675) and Chl.a concentration under three different irradiation intensities for M. aeruginosa and S. obliqnus. Power correlation could be best used to describe the correlations between a_ph (440), a_ph (675) and Chl.a concentration, while the linear correlation could be used to explain the relationships between a_ph (440), a_ph (675) and cell number. Meanwhile the specific absorption coefficients of M. aeruginosa and S. obliqnus fluctuated within small range in different irradiation intensities at different experimental periods, and increased with increasing irradiation intensity. A significant negative relationship was found between M. aeruginosa specific absorption coefficients at 440 nm, 675 nm and Chl.a concentration. However, the specific absorption coefficients of S. obliqnus had no relationship with Chl.a concentration mainly due to the composition and proportion of pigments and package effects. The average specific absorption coefficient integrated over the range of PAR (400-700 nm) of M. aeruginosa and S. obliqnus at three irradiation intensities of 5, 50, 100 μmol/(m²·s) are 0.0144, 0.0134, 0.0160 and 0.0086, 0.0088, 0.0105 m²/(mg Chl.a), respectively. The specific absorption coefficients of M. aeruginosa were significantly higher than those of S. obliqnus mainly due to the algae cell size of M. aeruginosa, 3.14 ± 0.43 μm, twice smaller than that of S. obliqnus, 7.24 ± 0.79 μm.