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Disentangling the relative roles of environmental and spatial processes in community assembly is a major task of community ecology. It is necessary to uncover this question at multiple spatial scales; however, the relative importance of spatial and environmental processes on ground-dwelling beetle assembly at a small scale is still unclear. Based on two permanent plots (each 300 m) located in primary mixed broadleaved-Korean pine forests, the topographic, soil, and plant factors were collected, and the spatial variables (MEMs, distance-based Moran’s eigenvector maps) were calculated. A redundancy analysis (RDA) was used to evaluate the influence of topographic, soil, and plant variables on ground-dwelling beetle compositions. A variation partitioning analysis was used to quantify the relative contributions of environmental and spatial processes on the assembly of ground-dwelling beetles. The results of the RDA reported that the soil, plant, and topographic variables affected Staphylinidae and Silphidae beetle compositions in both plots. According to the results of variation partitioning, pure soil and plant variables were important for the assembly of Silphidae beetles in the LS plot. The contributions of pure topographic, soil, and plant variables were significantly lower than those of pure spatial variables. The contributions of pure spatial variables were significant for the assembly of Staphylinidae and Silphidae beetles in both plots. In addition, the relative importance of environmental and spatial processes was not significantly changed after including more environmental variables and the unexplained variations. Finally, this study suggests that both spatial and environmental variables are important for the assembly of ground-dwelling beetle communities, while pure spatial variables are more important than pure environmental variables at a small scale (300 m).