为研究在长江口水环境问题日益突出的情况下，北支倒灌对南支水域水质的影响，以南支上段受北支倒灌直接影响的东风西沙水域为例，采用实测资料分析和数学模型计算结合的手段，就北支倒灌对南支水质的影响进行探讨。结果表明：一般情况下，北支水域水质条件劣于南支水域；北支倒灌明显影响东风西沙水域水质的时间为大潮期；北支倒灌污水进入东风西沙水域后，在可利用的淡水时段，部分项目的水质类别有所降低，北支倒灌对南支水域的水质有一定影响；鉴于北支倒灌的复杂性，需加强北支倒灌期南支水域与北支同步的水质监测。

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.