In the complex mountainous environment, it is valuable to explore the variation rule of soil pH for accurately managing soil pH and the sustainable use of soil. In this study, we collected 394,736 field surface soil samples and recorded the paired environmental conditions in Guizhou Province. The spatial autocorrelation, semi-variance model and geographical detector were employed to analyze the spatial structure characteristics and distribution pattern of soil pH. The results showed that the surface soil pH varies from 3.11 to 8.99, with the variation coefficient of 17.14%. Soil pH shows a patchy mosaic distribution pattern. The structural factors of climate, parent material, and topography play a determinant role in controlling pH differentiation. Geo detector analysis showed that the explanatory power of environmental factors for the soil pH differentiation is in the order of parent rock (0.0976) > altitude (0.0144) > soil temperature regime (0.0112) > land use (0.00503) > soil moisture regime (0.000812). The reciprocal effect of parent rock and altitude is noticeable.