Abstract: This study included four typical forest types in Beijing Songshan National Forest Park were selected as the research objects. According to the spatial order of atmospheric rainfall passing through forest ecosystem (forest canopy, litter layer and soil layer), the water quality effects of different forest types and different spatial levels were analyzed. The water quality characteristics and change mechanism were revealed. The results showed that: (1)The forest canopy exerted lympholysis on K⁺, Mg₂⁺, NH₄⁺ and Cl⁻ ions, and the forest penetration rain of each ion concentration increased by 0.01 to 2.88 times , and Ca²⁺, NO₃⁻, NO₂⁻, SO₄²⁻ and F⁻ were mainly retained by adsorption, with a concentration decrease of 4.21% to 60.08%, compared with the large gas rainfall. (2)The litter layer mainly leached K⁺、Mg²⁺, Ca²⁺, NO₃⁻, F⁻ and Cl⁻ ions, increased the ion concentration by 0.27% - 58.81%, and adsorbed Na⁺, NH₄⁺, NO₂⁻ and SO₄²⁻ ions, decreased the ion concentration by 1.21% - 49.76%. (3)The four kinds of forest traveling ion concentration change trend of soil as follows. Na⁺, Mg²⁺ and Ca²⁺ concentrations increased gradually with the increase of soil depth. K + , NO3-, NO2-, SO42-, and F-concentrations showed a trend of rising first after decreasing from 0 c m～20 cm soil layers, and subsequently decreasing with soil depth. (4)The most of ions is strong dissolve in 0 c m～20 cm soil layer. The concentration of Na⁺, K⁺, Mg²⁺, Ca²⁺, NO₃⁻, NO₂⁻, SO₄²⁻ and F⁻ ions in 0 cm - 20 cm soil layer increased by 10.14 times compared with that in dry water layer; The concentration of K⁺, NH₄⁺, NO₃⁻, NO₂⁻, SO₄²⁻, F⁻ and Cl⁻ in the solution of 20 cm - 60 cm deep soil layer decreased gradually, ranging from 16.64% to 80.92%. The results of this study provide an important reference for improving the ecological environment in Beijing, and provide theoretical basis and data support for the environmental governance around the Winter Olympic Games.