Taking a Korean pine (Pinus koraiensis) forest stand 37 years after selective cutting as test object, this paper studied the effects of selective cutting on the intra- and interspecies competitions among the major tree species in the stand. Selective cutting had significant effects on the population structure, distribution pattern, and competition index of the major species. There was a significant negative correlation between the changes of competition index and tolerance index of the tree species (r = -0.8821). The intra-species competition index had significant linear relationships with the aggregation index and the number of individuals. Heliophilous species Betula costata and Tilia amurensis had the largest aggregation index, and their intra-species competitions were stronger than interspecies competitions, being favorable to the coexistence of different species. Selective cutting weakened the competition of P. koraiensis with its companion tree species, while strengthened the competition of heliophilous species with other tree species. After 37 years of selective cutting, P. koraiensis varied little in its competition stress, being helpful to its regular growth. Because of self-thinning, the dominance of B. costata and T. amurensis had somewhat decrease. The competition stress suffered by Abies nephrolepis was weakened, being beneficial to its regeneration.