Comparative study of the growth characteristics and water purification effects of two free-floating macrophytes, water hyacinth (Eichhornia crassipes) and water lettuce (Pistia stratiotes), on domestic sewage contaminated water had been carried out using self-designed floating sinks. Results showed that the water lettuce has higher requirements on nitrogen and phosphorus concentrations, and the removal rates of phytoplankton and chlorophyll a by the water lettuce were respectively reached to 94.38% and 95.06%, which were significantly higher than those by the water hyacinth. The TN removal rate (82.08%), the net photosynthetic rate (27.90~20.28 μmol CO₂/(m^-2·s)), and the chlorophyll a content (1.05~1.08mg/g fresh weight) of the water hyacinth were respectively higher than those (they were 71.82%, 8.64~16.50 μmol CO₂/(m²·s) and 0.25~0.31mg/g fresh weight, respectively) of the water lettuce (P<0.05). However, when cultivated together with the water hyacinth, the water lettuce has higher reproductive ability and may have the risk of escape in engineering practice. In order to take full advantage of these two free-floating macrophytes in terms of water purification, a "sandwich" pattern for their cultivation was proposed. The results of this study would provide practical and theoretical references for the use of aquatic macrophytes for water purification and restoration in engineering practice.