Abstract: Based on the equation of Michaelis-Menten,the theory of nonlinear system was used to study the characteristic of freshwater algae in Tai Lake.Numerical study was used to research the effects of phosphorus on the growth of algae.It was found that within determinate initial value of phosphorus,the more the initial value of concentration of phosphorus,the more the biomass of algae and the sooner it reached the peak value.Via numerical study,we alsofound that the more the standing crop biomass,the sooner it reached the first peak value,but the time reached the peak value again was independent of the standing crop biomass.When the mortality of algal was changed,the character of the system was changed too,because the variation of concentration of phosphorus and the biomass of algae with time and the final stabile state of those were changed.The conclusion was that there was a stabile state while the growth of algal,the state was independent of the initial value of the system,but it was changed when the parameter of the system changed.