On the basis of phosphorus source investigation and transportation modelling, the phosphorus balance ivS studied and the phosphorus concentration dynamics predicted. In Gehu Lake, the total input for phosphorus ivS 270t/a, and output 174.5t/a, with a deposit coefficient of 35%. The main input ways are inflow current, cage aquaculture and feeding. The main output ways are outflow current, harvest of fish and harvest of aquatic plants. The models of phosphorus transportation processes show that Gehu Lake will remain mesotrophic under the maintenance of macrophyte biomass. Otherwise the phosphorus concentration would be raised, and algea will become dominent to make the lake eutrophic.