Understory species diversity results from the combined influence of various environmental factors. This study aimed to investigate the key factors affecting understory species diversity by focusing on four types of artificial forests in Qilaotu Mountain. Using Pearson correlation analysis, stepwise regression analysis, and variance decomposition, we identified the critical factors influencing species diversity and evaluated the explanatory power of the environmental factors involved.The results indicated that: (1) The understory species diversity in the four types of typical artificial forests was notably rich, encompassing a total of 43 families, 56 genera, and 68 species. The dominant plant families in the understory included Asteraceae, Rosaceae, Apiaceae, Poaceae, and Brassicaceae; (2) Among the four forest types, the mixed forest of Larix (larch) and Betula (birch) exhibited the highest level of understory species diversity, with 32 families, 45 genera, and 47 species. Significant differences were observed in species diversity indices when compared to the other three forest types; (3) Through Pearson correlation analysis and stepwise regression analysis, key factors influencing species diversity were identified as the non-spatial structure of the forest along with spatial structure-related variables, specifically diameter at breast height (DBH) and angle scale. Additionally, in terms of terrain factors, slope was determined to be a primary influencing factor. Soil factors such as soil moisture content and soil organic carbon were also found to be significant contributors to species diversity; (4) Further analysis using variance decomposition results demonstrated that both the non-spatial and spatial structures of the forest had the highest explanatory power for species diversity, while the explanatory powers of terrain and soil factors were relatively low.The implications of these findings suggest that to enhance understory species diversity in artificial forests, appropriate adjustments should be made to the DBH of the overstory trees. This can be achieved by managing the forest composition and structure to create more favorable conditions for understory growth. Additionally, actively promoting understory regeneration through various methods, such as controlled thinning, soil enrichment, and proper moisture management, can significantly contribute to increasing understory diversity.Overall, these results underscore the importance of understanding the ecological dynamics within artificial forest ecosystems. By effectively managing both the overstory and understory components, it is possible to foster a more diverse and resilient forest ecosystem that can support a wide range of species. This approach not only enhances biodiversity but also contributes to the overall health and functioning of forest ecosystems, which are vital for environmental sustainability and ecosystem services. Future research should continue to explore the intricate relationships between various environmental factors and understory diversity to further refine management strategies aimed at promoting biodiversity in artificial forests.