Using the floating plants water hyacinth(Eichharnia crassipes)to purify the polluted water has possessed the advantages of environmental protection, ecological and sustainable development. However, the algae blooms are frequently occurred in the summer and caused the massive nutrients(mainly phosphorus and nitrogen)accumulation, which often becomes the pollution sources of water body. It is vital of systematic studying the physiological adaptation mechanism to the adverse environment formed by the algae blooms gathered, and is helpful to reduce the adverse effects of algal bloom, in order to give full play the purification effects of aquatic plants. In this simulation, the change of key enzymatic activity of floating plant water hyacinth was studied as the algae cells gathered at higher temperature(water temperature>25℃). The environmental effects on the water hyacinth after algae cells gathered were studied at the same time, which are helpful to reveal the deep mechanism of floating plants in shallow-water ecosystem caused the algae cells dead. The results showed that the dissolved oxygen in water in the root-zone of plant consumed quickly and became anxious in 2h after algae cells gathered. The ORP decreased to lower -100mV in 1st day. It reduced to -199.9 mV and the water became the strong oxygen-reducing environment from the 2nd day to the end of the experiment. Concentrations of MDA, SOD, POD in leaf increased quickly after algae cells gathered, and the concentrations of the enzyme concentration of experiment treatment 2 in plant leaf rose to 2.17μmol/g(FW), 266.497U/g, 1988.60U/(g·min)at the end, respectively. However, the concentration of CAT in leaf reduced quickly during the experiment, and its content reduced to 6.09U/(g·min). Also the concentration of MDA and POD in the root of the water hyacinth declined rapidly and its content reduced to 0.57μmol/g(FW) and 525.161U/(g·min), respectively. But the content of SOD and CAT in root increased to 221.71U/g and 35.10 U/(g·min)during the period of the experiment after algae cells gathered. The changes of key enzymatic activity of the water hyacinth indicated that the adverse environment, which formed the anoxia, higher salinity, and strong stress environment after the algae blooms gathered, was harmful to the plant. A longer time(>5d)under adverse environment of formed algae cells had produced irreversible damage to the plants. The strong environmental impact after the algae cells gathered and decomposed on the aquatic plant is the key factors of the death of the plant. There should be avoided the algae serious accumulation of the algae blooms and aviate the injury of the cyanobacterial blooms to the aquatic plants, and we should give full play to purify the polluted water in the ecological restoration of the engineering practice by using floating plants.