According to field data from October in 2008 to July in 2009, variation feature of nitrogen and phosphate in Lake Poyang was analyzed. Regression analyses of NO₃^--N, NH₄⁺-N, and TP versus pH were carried out, and potential eutrophication of Lake Poyang was also assessed. It showed that inorganic nitrogen and phosphate in Lake Poyang varied in different months and different locations. Inorganic nitrogen and phosphate of lake areas were mainly affected by rivers and phytoplankton. April had the smallest N/P ratio, indicating that the mean-flow period was the major period on the growth and reproduction of phytoplankton. The upper reaches of Lake Poyang pollution was far less than the lower reaches and there was an increasing trend through lake area and the area out of the lake. Ratio of inorganic nitrogen to phosphate rose to 31.2 from 7.8 in October, then dropped to 7.4 in April, and rose to 8.9 in July. Inorganic nitrogen and phosphate versus pH show different correlation. For example, the correlation coefficient of inorganic nitrogen and pH even reached 0.5. Comprehensive analysis of the factors can be drawn. Potential eutrophication assessment indicates that during the survey period Lake Poyang can be classified as a phosphate-pollution nutrient area.