This paper analyzed the evolution trends of nitrogen and phosphorus concentrations of Lake Taihu for a period from 1985 to 2015. The result showed that there occurred water deteriorating at first years by records of the nitrogen and phosphorus indicators, and then the water improved in the whole Lake Taihu during the past three decades. The annual average of total nitrogen(TN) varied between 1.79 and 3.63 mg/L, and the thirty-year-average is 2.62±0.03 mg/L. The annual average of total phosphorus(TP) varied between 0.04 and 0.15 mg/L, and the thirty-year average is 0.086±0.001 mg/L. In 1996, the annual average of TN and TP concentrations in the whole Lake Taihu reached the historical peaks of 3.84 and 0.15 mg/L, respectively. Monthly records showed that, there was significant seasonal variation in the TN concentrations, in which the maximum usually appeared in March and April with the probability of 67% and 33%, respectively. The minimum usually appeared in four months between August and November, with the probability of 18%, 41%, 29% and 12%, respectively. However, the TP did not show significant seasonal variations. There were spatial changes in nitrogen and phosphorus concentrations in different areas of the lake. The water bodies in the western and northern showed greater changes than in areas of the eastern, southern and center. The long term changes in TN and TP of Lake Taihu are closely linked with the drainage economy development and the environment protection actions. As an example of Lake Wuli, a small water body in the northern Lake Taihu, there occurred remarkable decreases in the N and P concentrations in 2015 after many years of treatments such as water interception, water source control, and dredging and ecological restoration. The successful experience for Lake Wuli leads us to believe that it is possible to manage the small water bodies well, although waive for efforts on the improvement of the whole Lake Taihu.