Fixed sample plots were set up for researching competition relationships between Manglietia yuyuanensis and Cunninghamia lanceolata in 17-year-old M.yuyuanensis stands mixed wiht C.lanceolata. The interspecific competition intensity in different mixed stands was determined by using the competition indexes constructed with diameter of breast height, the volume of tree crown and distance between trees, through Hegyi’s Competition Index Model. The results showed that the spatial distribution of M. yuyuanensis in mixed stands was stochastic, the numbers of M. yuyuanensis and C. lanceolata around each M. yuyuanensis increased with the increase of the distance. Under the steady density, the ratios of C.lanceolata to M. yuyuanensis directly affect the interspecific competition and the growth. When the ratios of C.lanceolata to M. yuyuanensis were in the scope of 9-1 to 7-3, M. yuyuanensis had the obvious increase production trend compared with its pure stand. When the ratio was 9-1, the tree height and the diameter of breast height of M. yuyuanensis increase by 22.3% and 69.3% respectively; likewise, when the ratio was 8-2, they increase by 23.2% and 56.9% respectively, because at this ratio, the number of M. yuyuanensis in mixed stand was so low that its competition was mainly the interspecific competition from C.lanceolata. The competition index of M. yuyuanensis was 1.67 times lower than that in pure stand, especially the competition index constructed by the tree-crown volume was 21 times lower. however, when the ratios were in the scope of 6-4 to 5-5, M. yuyuanensis obviouly decreased production compared with pure stand, the intraspecific competition of M. yuyuanensis becomes stronger when its number increased. Based on the mechanism of stemwood cultivation, initial planting density of M. yuyuanensis trees should be reduced properly and higher ratio of C.lanceolata to M. yuyuanensis should be 8-2 or small higher in order to realize the cultivation goal of large timber of M. yuyuanensis .
