Abstract: According to the data of water resource quality bulletin and water resource bulletin of Changjiang River Basin in recent five years, the standard-reaching rate of water quality of first-class water function region and drinking water source area of second-class water function region in main streams and main tributaries of Changjiang River Basin was examined, and the change of main pollutants was also analyzed. Research findings are as follows:(1) in first-class water function region, the standard-reaching rate of water quality has improved apparently, of which the rate of river water quality is always higher than that of lake water quality. The standard-reaching rate of lake varies significantly during a year. (2) In second-class water function region, despite that the standard-reaching rate of water quality has raised by 11.6%, the rate of lake maintains a downward trend. (3) The standard-reaching rate of water quality has improved in main streams and tributaries of the Changjiang River, among which the Yibin-Yichang reach witnessed the most obvious improvement, followed by the Minjiang River and Tuojiang River. Except for the stream below Shigu of Jinsha River and mountainous rivers of the Jialing River, the standard-reaching rate of water quality in dry season is relatively poor in most river segments of the Changjiang River, indicating that the huge water environmental capacity of the Changjiang River contributes to the good water quality in recent years. The standard-reaching rate of river water quality in drinking water source area is relatively high, but varies sharply during a year. The rate of Yibin-Yichang reach and the main stream in the downstream of Hukou increases by 50.6% and 29.2%, respectively, while the rate of Wujiang River drops by 21.6%, with total phosphorus as the major standard-exceeding pollutant. (5) As the point-source pollution control works effectively, total phosphorus has replaced ammonia nitrogen and COD to be the most important standard-exceeding pollutant in almost all water bodies of the Changjiang River. In conclusion, further improving the water quality of Changjiang River requires precisely targeted, scientific and steady control of main pollutants in different water regions.

Key words: Changjiang River basin, water function region, standard-reaching rate of water quality, total phosphorus, water resource protection