This research aimed to understand the importance of biotic neighborhood and habitat factors for tree seedling abundance in broad-leaved Korean pine (Pinus koraiensis) mixed forest in the Changbai Mountain, northeastern China. We examined the relative effect of biotic neighborhood and habitat factors on seedling abundance by using generalized mixed linear model over 2 times. The results showed that a total of 10064 seedlings were investigated in all seedling plots of this site, belonging to 9 genera, 9 families, and 17 species. The abundance of Fraxinus mandschurica seedlings is extremely high, occupying an important position in the seedling composition. At the community level, heterospecfic adult effect, canopy openness, and herb density exhibited significantly positive effects on seedling abundance, while herb cover and soil moisture exhibited significantly negative effects on it. At the species level, the factors influenced the seedling abundance of Fraxinus mandschurica and Tilia amurensis were consistent with the results after screening at the community level. Heterospecfic adult effect exhibited significantly positive effects on Pinus koraiensis seedling abundance, but conspecific adult effect and canopy openness exhibited significantly negative effects on it. This study showed that biotic neighborhood and habitat factors together affected seedling abundance pattern, and the relative importance of biotic neighborhood and habitat factors varied among different seedling species.