Eutrophcation is becoming a world-wild question. In this process, aquatic macrophytes with different life form respond in different ways. The productivity of littoral emergent macrophytes as well as algae is becoming higher and higher, the high primary production of the lake accellerates the procees of transforming the lake into a terrestrial enviroment. In contrast, on submersed macrophytes are relatively stable and have the ability of removing nutrient from water and sediment. Lake Donghu is a Shallow Lake Situated in Wuhan, China. In the recent 30 years, population growth and increasing urbanization have led to the eutrophication of the lake. The structure of the lake ecosystem is simplified. Using Li-1800 underwater spectroradiometer to study the nature of underwater light field, the write obtains the Kd value and its spectral distribution, and calculate its optical depth. To compare the values of Kd. K_(440). K_(680) related to weed-type, algae-type lakes respectively, the advatage of using submersed macrophyte esp. P. maackianus in purifying the water body is evident. Study on the life history and the biologe of P. maackianus reveals its specificity in photosynthesis and in perennial growth. The experimental result forms the basis of subsequent works. In re-introducing the culture of P. maackianus into Donghu lake, the writer studied the effects of diffent environmental factors, and considers the uw-light limit, the effects of epiphyte colonization, the grazing effect of fish and the sediment condition to be limiting factors to the growth and colonization of submersed macrophytes. Studying the plant's tolerance to low-light condition, the writer noticed the physiological adoption and change in this process, and found isozyme method useful and promising practical works.