Abstract: The effects of nitrogen on the growth of Microcystis aeruginosa and Scendesmus obliquus were investigated with bulk culture, and the maximum special growth rate (μ_max) and semi-saturation constant (K_s) of them to nitrogen were calculated using the Monod Equation. The results show that the special growth rate of Microcystis aeruginosa and Scendesmus obliquus increased rapidly when the concentrations of nitrogen ranged from 0 to 2.00 mg/L,and from 0～4.00 mg/L respectively. μ_max and K_s of Microcystis aeruginosa and Scendesmus obliquus to nitrate were 0.23 d^-1, 0.14 mg/L and 0.41 d^-1, 0.24 mg/L respectively. According to dynamics constants, it can be expected that Microcystis aeruginosa will be dominant when nitrogen is scarce, while Scendesmus obliquus will be dominant when nitrogen is abundant.