Nowdays,the treatment of the sewage tends to become more and more diversified, biochemical treatment is a more conventional method of treating organic matter.However,it is only a handful to explore its intrinsic kinetic parameters from the theory of dynamics.By simulating the sewage biochemical treatment system,the mathematical expressions were obtained, which contained the ralitionship among the removal rate and degradation rate of organic matter, the concentration of activated sludge and the hydraulic stay time. The actual removal rate of organic matter was compared with the theoretical removal rate by using the process data of a sewage treatment plant located in Xiangtan.The results show that this model is very instructive for production.