Abstract: The atmospheric PM_2.5 samples were collected from June 2017 to May 2018 in Yanqing District, Beijing. The pollution characteristics of nine water-soluble inorganic ions in PM_2.5 were analyzed, and the sources were analyzed by SPSS software. The results showed that the average concentration of total water-soluble inorganic ions in PM_2.5 in Yanqing District was 28.0 μg∕m ³, of which S ${\mathrm{O}}_4^{2-}$ , N ${\mathrm{O}}_3^{-}$ and N ${\mathrm{H}}_4^{+}$ were the main water-soluble inorganic ions, accounting for 82.1%. Influenced by weather, the concentration of N ${\mathrm{O}}_3^{-}$ and S ${{\mathrm{O}}_4^{2-}}^{}$ was high in autumn and low in winter, while the concentration of N ${\mathrm{H}}_4^{+}$ was high in autumn and low in summer. Influenced by meteorological conditions and construction activities in winter, the concentration of Ca ²⁺, Mg ²⁺, Na ⁺ was the highest in winter. According to the charge balance analysis, the anions and cations in PM_2.5 basically reached equilibrium in spring, with weak acidity in summer and autumn, and weak alkalinity in winter. The mean values of SOR and NOR in PM_2.5 were 0.53 and 0.27, respectively, and there were obvious secondary transformation processes in the atmosphere. The ratio of N ${\mathrm{O}}_3^{-}$ ∕S ${\mathrm{O}}_4^{2-}$ was 1.66, which indicated that vehicle exhaust contributed a lot to water-soluble inorganic ions in PM_2.5. According to the correlation analysis between N ${\mathrm{H}}_4^{+}$ and S ${\mathrm{O}}_4^{2-}$ , N ${\mathrm{O}}_3^{-}$ , Cl ^—in PM_2.5 in Yanqing District, N ${\mathrm{O}}_3^{-}$ and S ${\mathrm{O}}_4^{2-}$ existed in the form of (NH₄)₂SO₄, NH₄HSO₄, NH₄NO₃ and HNO₃. Pearson correlation analysis using SPSS software showed that the correlations between any two of N ${\mathrm{O}}_3^{-}$ , S ${\mathrm{O}}_4^{2-}$ , N ${\mathrm{H}}_4^{+}$ in PM_2.5 in Yanqing District were strong, indicating that the secondary reaction was significant; the correlations between any two of Ca ²⁺, Mg ²⁺, Na ⁺ were strong, indicating that the sources of pollution may be the same; Cl ^- was strongly correlated with K ⁺, and Cl ^-mainly existed in the form of KCl in the atmosphere. Using factor analysis module to analyze the main components, it was found that the main pollution sources in Yanqing District were biomass combustion, dust pollution and motor vehicle exhaust emissions.