Abstract: To further analyze research succession and species composition of the mixed forest, a permanent monitoring plot of 21.84 hm² (420 m× 520 m) in forest region of Dapo Forestry Station of Jiaohe Forestry Experimentation Administrative Bureau was established, in which all trees were sized by diameter breast height (DBH) and mapped. There were 30310 genotype individuals and 32268 individuals with branch, belonging to 47 species, 28 genera and 18 families. The analysis of size-class distribution showed that pioneer species Acer mandshuricum, Juglans mandshurica, Acer mono, Pinus koraiensis, Ulmus macrocarpa, Ulmus japonica, Fraxinus mandschurica and Ulmus laciniata were obviously dominant species. Different species showed different structure types: partial normal, invert “J” distribution or even “L” distribution. The mean neighborhood pattern showed that different species and diameter classes had different spatial distribution patterns. All the individuals among the Pinus Koraiensis and Juglans mandshurica forest were randomly distributed, and other dominant tree species were clumped distributed; the rest were clumped distributed at different DBH classes except the random distribution of the Juglans mandshurica and the Acer mono with DBH above 10 cm and Pinus koraiensis with DBH below 10 cm. According to compositions and distributions of the species, there were abundant species of coniferous and mixed broad-leaved forest in Jiaohe, in addition, the community was at an early stage of succession, which had a high value of protection.