This paper presents the water nutrient absorption capability of canna plant (Canna generalis B.)at different phosphorus concentration and its applicabil ity as a water purification tool in floating culture system. Six test tanks with various phosphorus concentration, ranging from 0.01mg/l to 1.0mg/l, were used to measure the nutrient absorption and heat shielding rates of canna floating culture system. The experiment period was about 100 days, from June 25 to October 1, 2010. Important experimental results are summarized as follows:(a)canna grows more abundantly at higher phosphorus concentration;(b)T-P absorption rate of canna in water tanks with higher phosphorus concentration is greater than that in tanks with lower concentration, and the two factors are linearly correlated;(c)the floating culture system decreases DO concentration in tanks since it prevents aeration and blocks solar radiation through water surface;(d)the system also decreases the heat flux through water surface; and(e)the shielding rate of the thermal flux on the water surface highly depends on the material of raft, not on the growth stage of the plant.