A campaign of sampling atmospheric submicron particulate matter (PM₁) samples at Yizhuang zone in Beijing during July, October 2016 and January, April 2017, was carried out to investigate the characteristics of PM₁ and itswater-solublespecies during four seasons and different haze periods. The important factors affecting the formations of the secondary ions and haze pollution were discussed. The results showed that the average concentration of PM₁ reached 73.95μg/m³ for the entire study at Yizhuang zone, being 1.13times as high as the corresponding average concentration level of PM₁ in Beijing. Average concentrations of PM₁ in summer, autumn, winter and spring were 69.22, 63.38, 99.50 and 57.26μg/m³, respectively, showing the order of winter > summer > autumn > spring; the concentrations of PM₁ during haze days were 1.78~3.17times as high as those in clean days. The total water-soluble ion concentration in PM₁ was 37.30μg/m³, accounting for 50.44% of PM₁; secondary ions SO₄^2-、NO₃^- and NH₄⁺ (SNA) were the most important water soluble ions, which accounted for 86.98% of the total water soluble ions. The seasonal variation of the total water soluble ion concentrations in PM₁ was in accordance with SNA, following the order of winter > summer > autumn > spring. The average sulfur oxidation rate SOR was higher than the mean nitrogen oxidation rate NOR for the entire study, of which SOR presented the order of summer > autumn > winter > spring, and NOR showed the order of summer > autumn~spring > winter, and SORs and NORs in haze days were all significantly higher than those in clean days, especially in summer. The conversion of SO₂ to SO₄^2- was apparently influenced by relative humidity RH, temperature T, NO₂ and NH₃, and aqueous chemical reactions of SO₂ on the surface of PM₁ might be the important pathway of SO₄^2- formations. The conversion of NO₂ to NO₃^- was greatly influenced by RH, T, O₃, and NH₃. The haze pollution formation was mainly influenced by saddle type pressure field, even pressure field, and inversion layer, as well as weak air mass transport from the south, southeast and southwest directions.