Abstract: PM_2.5 samples were collected in Yinchuan City in autumn and winter of 2016 and spring and summer of 2017, and nine kinds of water-soluble ions (Na⁺, ${\mathrm{NH}}_4^{+}$ , K⁺, Mg²⁺, Ca²⁺, F^-, Cl^-, ${\mathrm{NO}}_3^{-}$ , ${\mathrm{SO}}_4^{2-}$ ) in PM_2.5 were analyzed to study the seasonal variation characteristics of water-soluble ions in PM_2.5. The results showed that the sum of the average concentration of nine water-soluble ions in PM_2.5 was (23.5±16.8) μg/m³, accounting for 24.1% of PM_2.5. The concentration of water-soluble ions showed the characteristics of high values in autumn and winter, and low values in spring and summer. The concentration order from high to low was ${\mathrm{SO}}_4^{2-}$ > ${\mathrm{NO}}_3^{-}$ > ${\mathrm{NH}}_4^{+}$ > Cl^-> Ca²⁺> K⁺> Na⁺> Mg²⁺> F^-. The proportion of SNA ( ${\mathrm{SO}}_4^{2-}$ , NO ${\mathrm{NO}}_3^{-}$ an ${\mathrm{dNH}}_4^{+}$ ) to the total ion concentration was 80.3%, and that to PM_2.5 was 20.2%. The contribution of SNA to PM_2.5 on heavy pollution days was 1.7 percentage points higher than that on non-heavy pollution days, which indicated that the higher the PM_2.5 concentration, the more serious the secondary pollution in the city. During the observation period, the average CE/AE of Yinchuan City was 1.4±0.8, and the average CE/AE of spring, summer, autumn and winter was 2.8±1.1, 2.0±0.4, 1.0±0.2 and 1.1±0.2, respectively, indicating that in spring and summer the contribution of basic inorganic cations to PM_2.5 was greater, and the cation and anion in autumn and winter were basically balanced. The results of the principal component analysis showed that the secondary inorganic sources, industrial sources and dust sources were the main sources of water-soluble ions in PM_2.5 of the city. The backward trajectory cluster analysis showed that the polluted air mass mainly came from the south during the observation period, and the particle concentration was higher. The air mass from the south was greatly influenced by the secondary pollution sources.