The data at 570 monitoring stations during 1990 were studied. The results indicate as follows: (i) the contents of nitrogen in the Yangtze mainstream has a raising trend from the upper reaches to the lower reaches; (ii) total nitrogen content at a lot of stations during the middle 1980s is 5-10 times more than that during the 1960s; (iii) seasonal variances of nitrogen content vary with watersheds; and (iv) the difference of nitrogen contamination level is related to the regional population and economic development.