Abstract: To investigate the influence of water intrusion from the north branch on the water quality of the south branch of Changjiang estuary, characteristics of water intrusion from the north branch  was studied on the basis of the statistics of measured water quality data and numerical model. Results indicated that: water quality of the north branch was worse than that of the south branch in general; the influence of water intrusion from the north branch on the water quality of the south branch was very obvious during spring tide; water quality of the south branch may become worse after water intrusion from the north branch. It's concluded that water intrusion from the north branch has a negative influence on the water quality of the south branch. Due to the complexity of water intrusion  from the north branch, water quality in both the branches needs to be monitored synchronously during the water intrusion.

Key words: Changjiang estuary, north branch, water intrusion, south branch, water quality