Abstract: Systematic investigations in various forms of N in the Yangtze River mainstream and major tributaries and lakes from the Yangtae River in the Yangtze upper reaches to the mouth were carried out from November to December 1997 (dry season),and in August and October 1998 (flood season).There were basic similar models in transport of various forms of N,their transport fluxes gradually increased from the river's upper reaches to the mouth and the most obvious were NO₃N 、 DIN 、 TDN and TN which were consistent with their stability extent.The export fluxes of various forms of N in the Yangtze River mouth came mainly from the middle and lower reaches,particularly in the dry season,and over half of N were contributed by the tributaries and the lakes and the maximum came from the Dongtinghu Lake,then the Poyanghu Lake water systems.In the transport and export fluxes in the dry and flood seasons,NO₃-N was major in three forms of inorganic N,DIN was major in various forms of dissolved N,and dissolved N was major in all forms of N.In the dry and flood seasons,various forms of N fluxes in the Yangtze River mainstream and tributaries and the export fluxes of various forms of N in the Yangtze River mouth were mainly controlled by runoff.The transport equations of various forms of N were suggested by this paper.