Lake Niushanhu is located in Wuchang County, Hubei Province, covering an area of 40Km~2. The species distribution and types of vegetation of the aquatic vascular plants were investigated during the period of 1989-1990. A total of 47 species of macrophytes belonging to 32 genera and 22 families were recorded. In general, the vegetation in the lake is dominated by Potamogeton maackianus which occupies approximately 90 percent of the lake area, almost comprising entire standing crop of the macrophytes. Experimental results indicate that the daily consumption rate of grass carp varies with water temperature and body weight of the fish, and the selectivity indices of the fish for P. maackianus were negative calculated by means of Ivlev's formula. Grass carp is in good conditions in lake Niushanhu. Its length-weight relationship may be given as W = 0.00002033L~(29747). The dynamic relationships between grass carp and P. maackianus are discussed in details. Coefficient of feeding pressure, C = F/P, was employed to demonstrate the state of grass carp - P. maackianus system. The rational carrying capacity and the optimum sustainalbe yields of grass carp are estimated as 1299.4 and 524.9 tons respectively, if 69.9 tons of large-sized fingerlings of grass carp were stocked every year.