[Objective] The soil microbial activity and its environmental influencing factors were researched to lay a foundation for the exploration of local microbial resources and the protection of a regional ecological environment.[Methods] The Ordos fieldspathic sandstone area was taken as the research object. Vegetation, soil, soil microbial quantity, enzyme activity, physicochemical properties, and vegetation-related indicators were investigated and analyzed. The interrelationship among the quantity distribution characteristics of soil microorganisms, soil ecological function, and vegetation diversity under a slope environmental gradient were also analyzed.[Results] ① Bacteria were the dominant group in the fieldspathic sandstone soil, followed by actinomycetes. Fungi were few. There were significant differences in the number of physiological groups of soil microorganisms among slope environmental gradients. ② Soil phosphatase, sucrase, urease, and catalase activities were different at different slope positions, and their contents were extremely low. There was a significant positive correlation between the fungal quantity and the acid phosphatase, as well as between the actinomycetes quantity and phosphatase and catalase. However, there was a significant negative correlation between the bacteria quantity and urease. ③ The particle sizes of soil water-stable aggregates were mostly concentrated between 0.25 and 0.5 mm. The particle size of 0.25 to 0.5 mm constituted a large proportion of soil in the shady slope, whereas the particle size of 0.106 to 0.25 mm accounted for a small proportion of soil in the shady slope. However, the sunny slope and gully bottom were the opposite of the shady slope. The soil moisture content was as follows: shady slope > gully bottom > sunny slope. The soil pH value and the contents of ammonium nitrogen, olsen-P, carbon, and calcium at the top of the sunny slope were higher than those for other slopes. The bacteria quantity was significantly negatively correlated with moisture content and calcium. The actinomycetes quantity was significantly negatively correlated with the pH value. ④ Environmental factors could account for 90% of the change of soil microbial quantity, among which the slope position and soil layer had the greatest influence (37.31%), followed by the vegetation factor (29.83%) and soil physicochemical properties (22.86%). Among the soil physicochemical properties, the aggregate particle size, moisture content, and pH value had a greater influence.[Conclusion] The slope position intensifies the differentiation of soil microorganism quantity and physiological groups, and the microorganism viability decreases as the environment deteriorates. The bottom of the ditch contains native vegetation and soil microbial resources for ecological restoration.