Competition among plants exists when resource availability falls below the sum requirement for optimal growth of the community. By studying the size structure and competitive relationships of mixed forest, the dynamics of community can be predicted. The size structure and competitive relationships of the Larix chinensis mixed-conifer forest type on Taibai mountain were studied. The results were as follows, ① The quantity of Larix chinensis seedlings and saplings was low, and the size structure indicated a declining population, while the quantity of Abies fargesii seedlings and saplings were relatively great, and the size structure indicated a growing population. ② For L. chinensis, the intraspecific competition intensity was stronger than interspecific; in A. fargesii the reverse was true, which implies that A. fargesii is the superior competitor. In the mixed-conifer forest, management activities, such as cutting non-target species, should be taken, so as to promote optimal environmental conditions for seedling recruitment in the rare L.chinensis.