Abstract: Through statistical analysis on water quality monitoring data of main monitored sections in the Three Gorges reservoir from 2006 to 2010，the general water quality of the reservoir before and after impoundment is evaluated with single factor method and the change characteristics of water quality is reflected by the ratio of monthly water quality classification to annual water quality classification． The analysis results show that if fecal coliform is not considered，the water quality in Yangtze River of Chongqing urban section will be good and the water quality classification of most monitored sections was III，accounting for 30 percent to 91． 7 percent; the ratio of III water classification of the main tributaries of Yangtze ranged above 70 percent，which means small variation of water quality． The content of SS dropped dramatically during mean water and dry period． The content of TP，CODMn and heavy mental have a close relationship with the drop of SS． Tp，CODMn and petroleum of a few sections in individual month and year exceeded the standard seriously．

Key words: Chongqing urban section, Yangtze River, Jialing River, water quality variation

摘要： 通过对重庆主城区两江江段2006—2010 年主要代表监测断面水质监测数据的统计分析，采用单因子评价方 法对试验性蓄水前后整体水质进行评价，以各月水质类别占全年比例的变化来反映水质变化。结果表明: 三峡水库 蓄水前后，在不考虑大肠菌群的情况下，长江河段干流重庆主城区水质状况总体较好，水质变化起伏不大，断面水质 大多为Ⅲ类，所占比例范围为30% ～ 91． 7%，长江支流嘉陵江河段两个断面Ⅲ类水质占70% 以上，说明库区水质指 标变化不明显; 平水期和枯水期时，悬浮物的浓度降低，TP、CODMn、重金属等也随之下降; 少数断面个别年月TP、 CODMn 和石油类污染物超标较严重。

关键词: 重庆主城区, 长江, 嘉陵江, 水质变化