Abstract: Precipitation samples were collected in Wuwei of Gansu from April 2013 to July 2014, and the major ions concentrations of the rainwater samples were measured, and the chemical characteristics of precipitation were analyzed using the correlation analysis, factor analysis, enrichment factor analysis and HYSPLIT trajectory analysis. The pH values of the precipitation were between 6.69 and 8.84, and its average value is 7.56. The electrical conductivity values of the precipitation was between 33.9 and 1 011 μs·cm^-1, and its average value is 191.07 μs·cm^-1. The order of the ion concentration in Wuwei was SO₄^2- > Ca²⁺ > NO₃^-> N a⁺ > Cl^- > K⁺ > Mg²⁺ > NH₄⁺ > F^-. Among them, SO₄^2-, Ca²⁺, NO₃^-, Cl^- and Na⁺ concentration accounted for 92.14% of the total ion concentration. The ion concentration changes with the seasons showed significant fluctuations, and the maximum values of Na⁺, Ca²⁺, NH₄⁺ all appeared in spring, and the maximum values of K⁺, Mg²⁺, F^-, Cl^-, NO₃^- and SO₄^2- all appeared in winter. The correlation analysis showed that pollution from human activity had a great influence on the ion concentration of the precipitation, especially emissions of pollutants such as SO₂, NO_x and chloride from industrial and agricultural production and other human activities. According to the distribution of water vapor flux and flow line and backward trajectory, sources of precipitation could be divided into two types:westerly wind source and mixed source (affected by the monsoon and westerly wind).

Key words: precipitation chemistry, environmental significance, chemical composition, Wuwei