Abstract: Abstract: Oxide ditch technology for wastewater treatment has been developed recently with such advantages as simple treatment flow, high stability, low capital construction investment and low operation cost. But the conventional oxide ditch still has many shortcomings as a type of deformation technology of activated sludge processes. For example sludge is easily suspending and expanding in the system, and single technology can bring lower removal efficiency on nitrogen and phosphorus (P). In order to solve these problems, a new type of oxidation ditch treatment system, plant-biofilm oxide ditch was developed in our laboratory, which combined the phytoremediation and biofilm technology with the oxidation ditch system and was applied to lake water surface for in-situ wastewater treatment. The simulation test and the plant-biofilm oxidation ditch small-scale experiment were carried out, and the removal of total phosphorus (TP), and the relationship between ferrum and aeration time, as well as the P absorption and removal by the ferric iron (Fe) plaque on the root surface of Canna generalis and Zizania cadaciflora in wastewater were investigated, in order to figure out the correlation between Fe in different forms and ferric iron plaque of plant root and P removal. Results showed that there was a close relationship between P removal and aerated time, Fe in different forms, ferric iron plaque of plant root in wastewater. The Fe3+ concentration of discharge water went up, but the P concentration descended after wastewater was treated by oxidation ditch system. When the aerated time was 1, 2, 4, 8, 12 and 24 h, the reduced amount of Fe increased by degrees on the whole with the extension of aeration time. When aerated for 12 h, the decline extent of Fe concentration in wastewater was very high, and the reduced amount of Fe was up to 0.45 mg/L. After the aerated time preponderated over 12 h, the decline extent of Fe concentration in wastewater was decreased. The relevance between the reduced amount of Fe and the aeration time reached a very significant level (P<0.01), while the correlation between the reduced amount of TP and the reduced amount of Fe also had a very significant correlation (P<0.01). In the small-scale test, the concentrations of P, Fe and Fe2+ in the effluent of 3 systems all decreased to some extent and the reduced amounts exhibited as Zizania cadaciflora system > Canna generalissy stem > control system. Additionally, the ferric iron plaque of Canna and Zizania root surface could absorb P. The deposition of iron oxide on the root surface of Canna generalis and Zizania cadaciflora increased with the operation time increasing, and the amounts of iron plaque and absorbed P on Zizania cadaciflora root surface both exceeded that of Canna generalis. The amounts of ferric iron plaque were up to 3096 and 1595 mg/kg respectively for Zizania cadaciflora and Canna generalis. The correlation analysis result showed that the relationship between P and ferric iron plaque on enrichment root surface had positive correlation (P<0.05). The experimental research provides theoretic and practical basis for the improvement, further application and generalization of plant-biofilm oxide ditch.