Abstract: Samples of atmospheric precipitation were collected during the period from September 2014 to August 2015 at the Yunlonggou Station in the water source region of the upper reaches of the Heihe River in Xi'an for analysis of ions the samples contained. Then characteristics and sources of the ions were explored through correlation analysis and with the enrichment factor method. The main cations contained in the samples were Ca²⁺ and NH₄⁺ and the main anions SO₄^2- and NO₃^-, which was similar to the characteristics of the precipitations in most urban areas of China. All the ions, except for NH₄⁺ and F^-, varied in concentration with the season, in an order of winter > spring > summer > autumn, which indicates that concentrations of the ions were related to their origins and amount of the precipitation as well. Correlation analysis of the ions and their origins indicates the correlation between SO₄^2- and NO₃^- was very high and both were affected by human factors; the correlation between Na⁺ and Cl^- was very high, too, because they are from the same source, i. e. sea; and so were the correlations between Ca²⁺, Mg²⁺ and K⁺ for they are all earth crust elements. Source analysis of the ions shows that human activities contribute 52.90%, more than half, of the ions in the precipitation, the earth crust does 38.43% and the oceans do 8.67%.