We investigated age structure and spatial distribution of Fagus crenata seedlings and saplings in a beech (F.crenata) forest stand. Every cohort of the seedlings and saplings showed spatially aggregated distribution and spatially associated relations were observed among the different cohorts. In order to explain environmental factors causing this spatial distribution, we evaluated effects of environmental conditions including coverage of dwarf bamboo, slope, topographical undulation, canopy closeness, and canopy closeness of F.crenata on the density of the seedlings and saplings, and causal-result relationships between the environmental conditions as well. The results showed that convexity significantly increased coverage of dwarf bamboo and coverage of dwarf bamboo significantly reduced the density of the seedlings and saplings. Therefore, it is likely that the change in coverage of dwarf bamboo caused by topographical undulation brings about spatially aggregated distribution of the seedlings and saplings.