Abstract: Based on the analysis of the observed hydrological data in March of 1996 in the Chagnjiang Estuary,the following results are concluded. In the North Branch, the velocity of the flood current is obviously larger than that of the ebb current, the residual current land-ward flows,and there exists serious saltwater instrusion from outer sea and from the upstream,i.e., from the North Branch, and is different with the variation pattern in regular estuary.The salinity is mainly influenced by the saltwater instrusion from outer sea during spring and early middle tide ,and by the saltwater instrusion from upsteam during neap and later middle tide. At the lower reachesof the South Branch, the the velocity of the ebb current is larger than that of the flood current and the ebb tide duration is longer than that of the flood. The maximum salinity occurs at the flood slack, and the minimum salinity occurs at the ebb slack.The salinity variation is affected by the saltwater intrusion from the outer sea, the hydrology obeys normal variation pattern in regular estuary.