In this study, spatial and temporal methods were used to conduct field survey sampling and laboratory analysis of litterfall decomposition and soil microbe characteristics in the adret and ubac slopes of the karst forest ecosystem in Maolan, Guizhou. To provide a scientific basis for the monitoring of nutrient cycling and dynamic equilibrium in forest ecosystems, we systematically investigated the characteristics of litter decomposition and soil microbial communities in different slopes, and revealed the relationship between litter decomposition properties and soil microbial communities. We found that the mass loss rate of the litter in the decomposition bag during the 1-year decomposition period was approximately 72%. During the litter decomposition process, the carbon element was released and the total nitrogen content of the litter showed a tendency for enrichment. The total phospholipid fatty acid (PLFA) content in the adret and ubac slopes during litter decomposition was highest at 180 and 360 days, with values of 559.2 and 513.6 nmol/g, respectively. The content of the soil microbial community was in the order of Bacteria (149.8 nmol/g) > Actinomycetes (63.9 nmol/g) > Fungi (31.3 nmol/g). In the adret slope the bacterial characteristics of 18:1ω7c increased mostly after 360-days decomposition, followed by cy19:0, and the characteristic fungal PLFA 18:1ω9c compared to before the decomposition. The PLFA content in the ubac slope showed a decreasing trend. After decomposition of 360-days, the bacterial characteristic fatty acid 18:1ω7c exhibited the greatest decrease of approximately 9.42 nmol/g, followed by i15:0 and the fungal characteristic fatty acid 18:1ω9c, together showing decreases of approximately 4.29-4.86 nmol/g compared to the decomposition of 90-days. Spearman analysis indicated that a positive correlation was found between the fungal community and the carbon release rate. Additionally, there was a significant positive correlation between the bacterial community and litter carbon and phosphorus release, and the effect of litter decomposition on the microbial community was greater in the adret than the ubac slope. Slope and litter nutrient release produced the most significant effects on litter decomposition and on the microbial community in the karst forest; moreover, the characteristic PLFAs 18:1ω7c, cy19:0, i15:0, and 18:1ω9c were observed to be the most sensitive to environmental changes.