TDS, pH and major ions in the Danjiangkou Reservoir, the water source area of the Middle Route of the South to North Water Transfer Project of China were monitored during the period of 2004-2006 to systemically analyze hydro-chemical characteristics and water chemistry type. Analysis of variance (ANOVA) and correlation analysis were performed to explore their spatio-temporal pattern. The results show that the water is of low mineralized degree with a total dissolved solid ranging from 149.9-291.2 mg x L(-1), and soft water with a total hardness ranging from 40-50 mg x L(-1) x HCO3- accounts for 77.54%-77.87% of the total major anions with a content of 122.5-170.0 mg x L(-1), while Ca2+ accounts for 70.66%-77.93% of the total major cations with a content of 37.1-43.2 mg x L(-1), and the water is of a HCO3- -Ca type. Major ions show similar spatial variations, decreasing downstream in the Danjiang Reservoir, and reaching the lowest values in the Hanjiang Reservoir. The temporal and seasonal variations of the hydro-chemical characteristics show that the concentrations of major ions in the dry season are larger than those in the wet season. Hydro-chemical characteristics in the reservoir are mainly determined by the rock weatherization, while and anthropogenic activities in the upper-stream and the reservoir region have been influencing the NO3- concentration. Finally, conservation strategies of water resource in the reservoir and its upper stream are discussed.