Abstract: The geochemistry of major ions(Ca²⁺，Mg²⁺，Na⁺，K⁺，HCO_3^2-
，SO4^2-，Cl^-，NO₃^-和SiO₃^2-)in the Yangtze River was studied, based on the monthly monitoring data at Xuliujing station for the period of 2004-2008 and the investigation result of the Yangtze River in September 2008. The study found that the concentration of main ions varies clearly in different seasons, with a negative correlation with the discharge of the River. But the difference of the concentration is less clearly than that of the discharge. There is a persistently increasing in the concentrations of K⁺, Na⁺, Ca²⁺, Mg²⁺, Cl^-, NO₃^-, SO₄^2-and the ratio of hardness/alkalinity; especially the concentration of SO₄^2-and the ratio of hardness/alkalinity have a more obvious increasing trend. In contrast, the concentration of SiO₃^2-and HCO_3^-show a decreasing trend. The changes of major ions mainly result from the environment acidification, the pollution emissions by human, the cyclic salt from sea, the preserved effect by reservoirs establishments etc.

Key words: chemical weathering, the Three Gorges Project, cyclic salt, industrial pollution, the Yangtze River, chemical weathering, the Three Gorges Project, cyclic salt, industrial pollution