Abstract: The purification effect of Hydrilla verticillata for urban river water was simulated. The results showed that compared with the still water condition, under the moving water condition with water flow of 1.74 cm/s, Hydrilla verticillata had the superiority in purification of NH₃-N, TP and COD_Cr, with the average removal rate of 92.03%, 83.08% and 74.04%, respectively. After the experiment, the original surface water was purified from Classification V to Classification III, according to the Environmental Quality Standards for Surface Water (GB 3838—2002). The biomass of Hydrilla verticillata of the moving water group was greater than that of the still water group, demonstrating that the Hydrilla verticillata grew better under low water-flow condition and had better purification effect, compared with the still water condition.