This paper aimed to study the spatial pattern of main tree seedlings and its relationship with environment factors in a secondary poplar-birch forests in Changbai Mountains of northeasten China. All tree seedlings with DBH<1 cm within a 5.2 hm² (200 m×260 m) plot were mapped in 2008. The spatial pattern of 5 tree seedlings was investigated, and the relationship between spatial pattern of tree seedlings and environment factors was analyzed. The results indicated that on small scales, Fraxinus mandshurica (0-90 m), Acer mono (0-60 m), Tilia amurensis (0-60 m,90-150 m), and Acer pseudo-sieboldianum (0-90 m) showed significantly spatial autocorrelation, that is, there was an aggregated pattern. The environmental variables and spatial variables showed strong interpretation on spatial variation of seedlings at the community level, with an explanatory power of 61%. Pure spatial variables exhibited strong interpretation power of 56% while pure environmental variables accounted only about 1%. The spatial pattern of Fraxinus mandshurica was significantly correlated with soil organic matter, soil moisture, and total K. The spatial pattern of Acer mono was significantly affected by soil moisture and total P. The spatial pattern of Tilia amurensis was significantly influenced by total P. The spatial pattern of Acer pseudo-sieboldianum was significantly affected by soil moisture. However, no environmental factor had significant effect on spatial variation of Acer barbinerve. Most of the main tree seedlings showed an aggregation pattern, and environmental factors had a certain influence on their distribution.