Abstract: The self-developed experimental device of a cuboid sink welded with stainless steel (10.0 m × 1.0 m ×0.5 m) without the top cover was used to investigate water purification of open pond contaminated with domestic sewage using biological floating island growing with Acorus calamus L. and Eichhornia crassipes, and the fates of nitrogen (N) and phosphorus (P) in the water purification system. The results revealed that the removal rates of algal density and chlorophyll a were over 90%, and the removal rate of COD_Mn concentration was over 45%. Total nitrogen (TN) and total phosphorus (TP) concentrations of the polluted water by running through the 10 m sinks decreased from 3.71 and 0.24 mg/L to 1.71 and 0.09 mg/L by E. crassipes, and to 2.69 and 0.16 mg/L by A. calamus, respectively. The main fate for N and P in the purification system with E. crassipes was absorbed by the plants, which accounted for 84.31% and 77.52% decrease of the TN and TP, respectively; while the N and P absorbed by plants in the system with A. calamus only accounted for 7.72% and 8.55% reduction, respectively. A large proportion TN (35.26%) and TP (51.58%) existed in the sediments in the sinks with A. calamus, while location of over 57% and 39% of the TN and TP were unclear in the system, which may relate to the biofilm growing on the floating island. This study provides practical and theoretical references for ecological restoration of open pond contaminated with domestic sewage using phytoremediation technology with floating island and E. crassipes.