Competition is an important factor in biology and plant-plant interactions has inspired an increasing concern in recent years. In plant communities, competition is defined as the interaction between individuals, brought about by limited resources. Aboveground competition is usually size-asymmetric: the bigger individuals have a disproportionate advantage in competing for light than the smaller ones. This study deals with biomass allocation patterns and aboveground competition influences on biomass partitioning and allometric equations of understory Korean pine (Pinus koraiensis). The results will contribute to understanding the mechanisms of aboveground competition and provide a theoretical guide for effective utilization and protection of Korean pine. The results show that: (1) When dividing live crown into three equal layers (top, middle and bottom), live branch biomass increased from the top to the bottom layer, while needle biomass was highest in the middle and bottom layers of the crown. However, there was no significant difference between the needle biomass located at the middle and bottom layers (P>0.05). The relative proportion of coarse root (>5 mm) biomass increased while that of small fine root (<2 mm) and coarse fine root (2-5 mm) biomass both decreased with increasing total belowground biomass. (2) Stem diameter at breast height and tree height both showed a significantly exponential correlation with aboveground competition intensity (P<0.001). Breast-height diameter and tree height both decreased with increasing competition intensity. The ratio of tree height to breast-height diameter showed a significant linear relationship with competition intensity (P<0.05), whereas, there was no significant relationship (P>0.05) between competition intensity and crown ratio, which is defined as crown length divided by total tree height. (3) With increasing competition intensity, the relative proportion of stem biomass deceased while that of fine root (small fine root and coarse fine root) biomass increased. There was no significant relationship between competition intensity and the proportion of live branch, needle as well as coarse root biomass (P>0.05). (4) The average root to shoot ratio value was 0.15. This ratio was not affected by competition intensity (P>0.05). Similarly, the stem to needle biomass ratio also did not correlate with competition intensity (P>0.05). (5) Aboveground competition significantly affected the biomass allometry of aboveground biomass components and competition intensity showed a significant negative (P<0.001) correlation with biomass components. Thus, competition should not be disregarded in biomass studies. Regarding forest management, it is necessary to carry out tending operations to release the understory Korean pine trees from competition, in order to stimulate their growth, to obtain timber products and to protect the available germ plasm resource.