Fallen logs are essential structural and functional components of the forest ecosystem, but the decomposition of fallen logs is very slow. Until recently, there has been a lack of knowledge about the effect of fallen logs on soil biological properties. The objective of this study was to determine the temporal and spatial distribution patterns of soil enzyme activities under fallen logs and how they were influenced by environmental variables during log decomposition in the Tianbaoyan National Nature Reserve. A multivariate analysis was performed to investigate the connections between environmental variables and soil enzyme activity. This study took place in Tsuga longibracteata forest, which is in the Tianbaoyan National Nature Reserve, Fujian Province, China. In the forest, the coefficient of variance for soil enzyme activity shows a high degree of variation. The cellulase spatial distribution pattern showed the greatest change, whereas changes to protease, urease, and invertase activities were lower. The increase in decay class caused a decreasing trend in protease and urease activities, but cellulase activity increased. Soil enzyme activities were positively associated with soil organic carbon (SOC) and total nitrogen (TN). Among the environmental variables, soil chemical properties had the greatest effect on soil enzyme activities, which suggested that soil chemical properties should be taken into account when assessing the effect of fallen logs on soil enzyme activity. These activities were positively associated with TN, SOC, elevation, and slope. We identified the interactive relationship between fallen logs and soil enzyme activities and showed that the presence of fallen logs plays an important role in forest C recycling.