【Objective】 Soil acidification is a prominent issue in the typical black soil region of the northern Songnen Plain, which hinders the sustainable development of regional agriculture. Thus, exploring the characteristics of soil pH, exchangeable acidity, and their influencing factors in the cultivated soils of the typical black soil region can provide a scientific basis for the zoning and classification of soil acidification improvement measures. 【Method】 In this study, surface soils of cultivated land in Bei'an City and Wudalianchi City, Heilongjiang Province, were taken as the research object. Soil samples from 119 soil sites were collected to determine soil acidity and related soil properties, while data on relevant environmental and anthropogenic factors were collected. Pearson correlation analysis and random forest model were used, combined with the theory of soil acid-base buffering, to explore the main controlling factors affecting the spatial variation of soil pH, exchangeable H?, and exchangeable Al3? contents. 【Result】 The results showed that the surface soils of cultivated land in the study area were dominated by strongly acidic and acidic soils. The spatial variability of soil pH was low, while the spatial variability of soil exchangeable acid content was high. There were no significant differences in soil pH and exchangeable acidity contents between dark brown soils, black soils, marsh soils, and meadow soils. Pearson correlation analysis indicated that soil pH was extremely significantly and positively correlated with the contents of exchangeable Ca2? and Mg2?, clay fractions, and mean annual temperature, and significantly negatively correlated with soil organic matter content, silt content, aluminum saturation, mean annual precipitation, and elevation. Soil exchangeable H? and Al3? contents were extremely significantly and positively correlated with soil organic matter content, silt content, aluminum saturation, mean annual precipitation, and elevation, and extremely significantly and negatively correlated with the contents of exchangeable Ca2? and Mg2?, clay fractions, and mean annual temperature. The random forest model showed that the 15 influencing factors explained 84.38% and 71.61% of the variations in soil pH and exchangeable acids, respectively. Among these factors, soil factors contributed the most (65.67% and 56.19%), followed by environmental factors such as annual average precipitation (18.57% and 13.87%), whereas the contribution of anthropogenic factors was negligible with respect to the spatial variation of soil pH and exchangeable acid (0.14% and 1.55%). 【Conclusion】 The typical black soil region in northern Songnen Plain has a high acid buffering capacity due to its high base saturation and abundant feldspar minerals, which is significantly different from the soil in typical red soil regions. The main controlling factors for the spatial variation of soil acidity are soil exchangeable base ions (Ca2? and Mg2?) contents, aluminum saturation, and annual average precipitation.