Abstract: Based on the data of 9 monitoring variables in 5 monitoring sections of Changsha section of Xiang River, with the use of synthetical index method, pollution share rate, and TLI method, analyzed the water environment parameter changing of Changsha section after the preliminary stage water retaining of multipurpose hydraulic project in Xiang River. The result shows that, the comprehensive pollution index level, pollution share rate and nutrient content level of the 9 monitoring variables, which are ammonia nitrogen, permanganate, total phosphorus(nutriment), volatile penol, petroleum(organic poison), mercury, arsenic, lead and cadmium(heavy metals), in 5 monitoring sections are in varying degrees of declining in both time and space scales, and the XMPI demonstrated a most obvious decline. The reasons of the improved water environment in Changsha section are: ①the optimization and adjustment of economic structure of Changsha city; ② the synchronous construction of Changsha multipurpose hydraulic project and the engineering of the pollution treatment; ③ the water retaining ability of Changsha hydraulic project. When the retaining water reaches the normal level, the lowest water level in Changsha section rises 1.5 m, and makes the average water level of sections of Changsha, Xiangtan, Zhuzhou rises 4-6 m, 2-4 m, and 1-2 m correspondingly, thus increased the volume of water of Changsha section, and can dilute, degradation and transport the pollutant in water.

Key words: Changsha multipurpose hydraulic project in Xiang River, monitoring sections, water environment parameter