In this paper, 70 fixed plots of 20 m×30 m were setting in the eastern section of Pinus koraiensis plantations under different site conditions in the temperate humid climate zone. In addition, the tree height, diameter at breast height, crown width and forest nutrients of the trees in the sample area were measured. In each sample plot, 5 dominant trees with the highest and better growth were selected as the object trees. The corresponding competitive trees of the object trees were determined by Voronoi diagram, and the distance between the dominant trees and the competitive trees in each plot was measured. Using Hegyi single-tree competition index model, we analyzed the dominant trees in different levels of intraspecific competition intensity, and explored the growth factors, terrain factors, and soil nutrient factors on the influence of the dominant tree competition index. In addition, stand growth factors, topographic factors, soil nutrient factors, and the competitive index of dominant trees were fitted and the correlation was analyzed. The results showed that the competition intensity of Pinus koraiensis decreased with the increase of the diameter at breast height of the dominant trees, and the relationship between them followed a power function. Moreover, the competitive index of dominant trees of Pinus koraiensis was significantly correlated with height, diameter at breast height and crown width (P <0.01). Slope aspect, slope position and altitude had significant effects on the competition index (P <0.01). The competitive index of dominant trees in Pinus koraiensis forest was significantly correlated with soil N, P and K content (P <0.01). The influence of pH value on the competitive index of dominant trees was not significant. When the diameter at breast height of Pinus koraiensis forest reached 45 cm, the tree height was higher than that of the surrounding competitive trees, and the crown width was larger than that of the surrounding competitive trees. With the increased of the utilization of surrounding resources, the natural thinning of trees would occur and the competitive pressure would decrease. Pinus koraiensis liked light and water, which led to its competition index in the shady slope was bigger either uphill or downhill, and the growth of Pinus koraiensis forest was better from top to bottom. By reason of the foregoing, large diameter timber cultivation of Pinus koraiensis plantations should be planted on the middle or lower slopes of semi-shady and semi-sunny slopes, with fertile soil and good permeability.