A total of 18 fixed plots were chosen to investigate tree point information within Cunninghamia lanceolata ecological forests in Fushou Forest Farm, Pingjiang County, Hunan Pro-vince. The weighted Voronoi diagram was generated based on the effect weight of DBH, tree height and average crown diameter on forest competition zone determined by using grey relational degree to determine tree competition unit. Accordingly, we put forward W_V_Hegyi competition index that can reflect forest competition more scientifically and that was used to analyze intraspecific and interspecific competition within and between C. lanceolata (dominant species) and other associated tree species. The results showed that the effect weights of DBH, tree height and average crown diameter on forest competition zone were 0.38, 0.29, and 0.33, and the number of competitive trees towards one single object tree ranged from 2 to 14 with 13 possible values in the tree competition unit determined by the weighted Voronoi diagram. According to the simulation effect of curve model based on competition index and DBH of target trees, W_V_Hegyi competition index was better than Hegyi competition index and V_Hegyi competition index. The competitive pressure of dominant species (C. lanceolata) mainly came from intraspecific competition. The average intraspecific competition indexes of C. lanceolata in 3 age groups (young forest, middleaged forest and nearmature forest) were 1.36, 0.99, and 0.63, and the average interspecific competition indexes of the 3 age groups were 0.87, 0.82, and 0.46, respectively. The average intraspecific competition indexes were 1.56, 1.37 and 1.21 times of interspecific competition indexes, respectively. The competition pressure of other associated species mainly came from interspecific competition. Since the proportion of these species was very small, they had little effect on the competition situation within whole C. lanceolata ecological forest stands.