Fallen wood is an important component of the forest ecosystem, which plays an important role in ecological conservation, biodiversity maintenance, and forest renewal. Its decomposition regulates the nutrient cycle of the soil and often changed to changes in microbial community structure of the soil. Therefore, quantify the influence of the fallen wood on soil fungus community and distribution is very significance. However, there are few reports about the effects of decomposition of fallen wood on soil microbial community, especially in Maolan kast evergreen broad-leaved deciduous mixed forest, a rare remaining subtropical karst forest with strong original in China and even the world. In this paper, the fallen woods of four common tree species (Machilus rehderi, Liquidambar formosana, Cyclobalanopsis glauca, and Platycarya longipes) that are in mildly, moderately and severely deciduous decay levels in Maolan's evergreen and deciduous broad-leaved mixed forest in Guizhou are selected as the research object. Three different horizontal distances (10 cm, 30 cm, and 50 cm) from the outer edge of the fallen wood were used to analyze the effects of tree species, decay grade and distance on the types and abundance of soil fungi community. The results show that:1) the soil fungi affected by the fallen woods of the four tree species in the karst forest are mainly Ascomycota, Basidiomycota and Mucor in the phylum classification, and the dominant genera are Mortierella spp., Phlebia spp., Pluteus spp. and Chaetomium spp., etc; 2) Different tree species of fallen woods have different effects on the relative abundance of soil fungi communities. The soil fungi richness Chao1 index under the fallen wood of the Platycarya longipes is significantly higher than that of Cyclobalanopsis glauca; 3) With the deepening of decay, the soil fungal community diversity under the fallen wood of the four tree species showed a significant increasing trend; 4) The abundance of soil fungal communities changes significantly with the increase of the distance from the fallen wood (10- 50 cm), such as Pluteus spp., Mortierella spp. and Ganoderma spp. are affected by Machilus rehderi, Chaetomium spp. of Liquidambar formosana, Mortierella spp. of Platycarya longipes, Phlebia spp. and Oliveonia spp. of Cyclobalanopsis glauca, etc. This study quantified the soil fungal communities composition and distribution patterns affected by fallen woods in karst forests, and provided a scientific basis for further exploration of the mechanism of interaction between soil microbial communities and fallen wood decomposition to some extent.