ObjectiveTo explore the impact of primary forest conversion on soil microbial community diversity, structure and functions, in order to provide a theoretical reference for soil health preservation.MethodsA subtropical typical primary evergreen broad-leaved forest and the adjacently converted conifer plantation, orchards, sloping tillage, and rice paddy were chosen in northwest Hunan Province. We assessed the response of the bacterial and fungal genomic diversity, community structure, and predicted functions to primary forest conversion.ResultsComparing to the primary forest, the bacterial diversity was increased by 29%—34% in cultivated lands, while the fungal diversity was decreased by 42%—49% in the orchards. The response direction and magnitude of soil bacterial and fungal predicted function depended on the specific soil function and converted land-use type. Comparing to the primary forest, the relative abundance of global and overview maps, carbohydrate metabolism, and metabolism of cofactors and vitamins were 9%—25% higher in orchards and croplands, while the relative abundance of membrane transport, signal transduction, cellular community-prokaryotes were 11%—27% lower in orchards and croplands. In sloping farmland soil, the relative abundance of endophyte-litter saprotroph-soil saprotroph were 32%—42% lower than those in the primary forest, while the animal pathogen and plant pathogen were 10%—397% higher than those in the primary forest. There was no significant difference in > 50% of the relative abundance of predicted microbial functions between the primary forest and plantations. The predicted bacterial functions are mainly regulated by soil moisture and labile organic C content, whereas the predicted fungal functions are mainly regulated by soil pH, quantity of labile organic C, and nutrient availability.ConclusionThis study suggests that the conversion of primary evergreen broad-leaved forest to Cunninghamia lanceolata plantation is relatively conducive to the maintenance of soil health and functional potential, whereas the conversion to sloping farmland can increase the risk of soil-borne diseases on crops. Our findings provide a theoretical basis for predicting regional soil health evolution and rational land planning.