Abstract: The Ganjiang River, originated from Jiangxi Province in southern China, is a tributary of the Yangtze River. In order to investigate the ion chemistry, runoff effects and controlling mechanisms of the Ganjiang River, its water chemistry data from 1958 to 2016 was collected and analyzed. The results were as follows: the major ions in the river were Ca2+, Na+ +K+, HCO-3♂ and SO2-4，the pH value was 6.0~8.8, the TDS range was 15.7~141 mg/L, and the monthly variation of all ion concentrations were positively correlated with river runoff. The positive correlations between river runoff and the monthly variation of SO2-4, NO-3♂ and Cl- before 1980 were higher than that after 1980, indicating that chemistry ion came from non-point sources pollution before 1980, but many sources appeared after 1980. The proportion of sea salt source Cl- to river water Cl- was less than 19%, the sulfuric acid was involved in the weathering of silicate rock and carbonate rock, reflecting the strengthening of human activities after 1980. The increase of Cl-/(Na+ + Cl-) and SO2-4/(Na+ + Cl-) were related to the total domestic production, population, coal consumption, fertilizer utilization and waste water discharge. According to the World Health Organization standards, the water quality of the Ganjiang River can be used as drinking water. Nevertheless, continuous increase of Cl- and NO-3♂ concentrations after 1980 should be payed attention to.