Soil fungal communities play important roles in soil ecological processes. However, biogeographic patterns of soil fungal communities and the underlying mechanisms shaping these patterns are still not fully understood on the Qinghai-Tibet Plateau. We conducted extensive soil sample collections in three regions differing in their aridity with different environmental conditions across an area spanned 2199 km in width and 1249 km in length in the Qinghai-Tibet Plateau (QTP). We investigated the biogeographical patterns of soil fungal diversity and the key factors shaping them. Null model analysis showed that the fungal species turnover processes linked to environmental selection predominantly govern the heterogeneity of fungal communities across the QTP. NDVI, which is primarily influenced by local climate, serves as a direct indicator of fungal community diversity. In arid and hyper-arid regions where the plant community remains stable, alkaline conditions lead to lower fungal species diversity. Conversely, low-pH environments in warm and humid regions were related to higher fungal species diversity. Our findings underscore the pivotal roles of plant and soil pH in response to climate fluctuations on the diversity of soil fungal communities in QTP.