To investigate the characteristics of nitrogen, compare different nitrogen forms in different systems and analyze the relations of nitrogen and environmental factors, twenty-eight surface water samples and twenty-two sediment samples were collected from the largest man-made lake system in Shanghai in spring of 2013 to examine the contents of nitrogen. By simulating experiments on the effect of salinity in the overlying water, the exchange of ammonia and nitrate in the sediment-water was analyzed. The results indicated that average level of nitrogen in Dishui Lake system was high. The spatial differences of nitrogen in the surface water were smaller than that in the sediment. Nitrate was the main form of inorganic nitrogen in the water and organic nitrogen was the main nitrogen form in the sediment. The contents of nitrogen in rivers around the Dishui Lake were higher, suggesting that this river water was one of the main nitrogen sources of the Dishui Lake. The simulated experiments showed when the salinity in the overlying water was increased, the content of nitrate released from the sediments to the water would increase and tend to balance out with each other. but the content of ammonia released from the sediments to the water would decrease then reach a stable staye.