According to the data observed in a China-Japan Joint Investigation,the parameters of an ecosystem dynamics model (Qiao et al.,2000) were optimized.The values of eighteen parameters for the model were obtained,with nutrient haft saturation constant,Kn=1.4 μmol/dm3,Kp=0.129 μmol/dm3 and Ks=1.16μmol/dm3 for the diatom and Kn=0.345μmol/dm3,Kp=0.113 μmol/dm3 for the flagellate.Three proposals to set up a function for this multiple objective problem were discussed in detail.