In this study, the intraspecific and interspecific relationships of a 15-year-old Larix principisrupprechtii plantation were analyzed in Mt. Taiyue, Shanxi province, by using niche theory and Hegyi individual competitive index model. The results showed that: (1) niche breadth for L. principisrupprechtii and Betula platyphylla were larger than that of other tree species. There was a high proportion of niche similarity but low degree of overlap between L. principisrupprechtii and B. platyphylla, indicating the abundant environmental resources and the existence of low resource utilization competition. (2) By the calculation for Hegyi competition index, we found that the effect range of competition of L. principisrupprechtii in this area was 6 meters. The competition intensity to L. principisrupprechtii ranked as B. platyphylla > L. principisrupprechtii (intraspecific) > Picea koraiensis > Salix caprea. The competition intensity of L. principisrupprechtii decreased with increasing the diameter of breast height (DBH). (3) The nonlinear fitting result of the power function was optimum to predict the competition intensity of L. principisrupprechtii with different DBH. The model prediction showed that the community reached a stable stage and the competition intensity changed insignificantly at DBH of 60-70 cm for L. principisrupprechtii. (4) The Godron stability index was 39/61, which was far away from the stable point 20/80. This result manifested the high competition intensity in future; (5) A new partition method defining the effect range of competition was proposed, which could divide inside radius and outside radius accurately by calculating average competitive intensity of each tree in the unit area of competitive sample circle. The method would provide a more visual and precise result.