A new type of ecological floating bed was developed that combined hydrophyte, aquatic animal and biofilm. The dynamic pilot study on purification characteristic and mechanism of the floating bed for eutrophic was carried out. Result shows that the removal efficiencies of TN, TP and COD(Mn), are 53.8%, 86.0% and 35.4% respectively under the water exchange period of 7 days. Main purification role is played by artificial medium and aquatic macrophyte in pollutants removal, but the Corbicula fluminea introduced to food chain of combined floating bed enhances the purification effect through the ways as follows: improving the resolvability, ammonification and biodegradability of particulate organic matters, meliorating the substrate supply condition for absorption of plant and degradation of microorganism attached on artificial medium, hastening the growth and activity of microorganism.