Abstract: This article used the actual database to count the change in shape of lake basins and in the flood of Poyang Lake in 50 years. It is indicated that because of reclamation, the lake area experienced a reduction of 1 300 km2 during the period from 1954 to 1992, and the volume had a reduction of 81×108 m3, with the regulating coefficient dropped from 17.3% to 13.7% and regulating flood ability reduced by 20.8%. When comparison was made between 1990s and 1950s, the average value of annual maximum high water raised 1.80 m. It was also calculated that the maximum high water level by means of restoring lake area from cultivation would be reduced by 0.72 and 0.68 m, respectively in two serious flooded years, i.e. 1954 and 1998. The restoration may also have some influence on the frequency of flood levels in Poyang Lake, a 0.63 m and a 0.68 m reduction in maximum high water level may be expected in one chance flood within 50 years and one chance flood within 100 years, respectively. It is also indicated that restoring lake from cultivation at high water level, the socalled semirestoration can reduce the flood level, and is closely related with waterlogging degree before restoration. Major questions in relation to lake restoration by stopping cultivation are: waterlogging capacity in dike areas when restoration was taken at high water level, and schistosomiasis problem in turning over dykes for flood area, the socalled complete restoration. The countermeasure to solve these two problmes are: “limiting the high and reinforcement, evacuating for gathering” in semirestoration dikes and “opening to discharge the flood, pay attention to the cure of schistosomiasis” in the doubledrawsback dike.

Key words: restoring lake by stopping cultivation, semirestoration, complete restoration, flood effect