The restoration of eutrophic water by using aquatic plants has become a major method of ecological restoration of water bodies. Thus, in this work, various indicators of water were studied by using Water caltrop which was growing in the northern Taihu Lake. The results indicated that the average concentration of TN and TP were 1.64 mg/L and 0.049 mg/L inside the planting area where the water purification project was carrying out, which were lower than outside (3.08 mg/L for TN and 0.127 mg/L for TP). Because of the constantly absorbing nutrients from the sediment, as well as the microbial nitrification and denitrification happened on the roots. Meanwhile, so the concentration of TN, TP, NH4+ -N and NO3- -N inside the planting area were also below outside. When the water purification project was interrupted, the concentration of transparency, chlorophyll a inside the planting area was higher than that of outside, which indicated that Water caltrop had a relatively strong capacity on water purification.