Competition has an important impact on tree growth. Competition index is widely used to quantitatively describe the competition relationship among trees. In this study, the arbor forests were taken as the research objects in Lin'an of Hangzhou city, Zhejiang Province. Based on the Hegyi Competition Index of Voronoi diagram, the competition relationship of various forest types was analyzed at regional scale in Lin'an in 2004. The results showed that at the level of single tree, the total competition index, intraspecific competition index, and interspecific competition index of individual trees of different forest types were the largest at diameter at breast height 5-10 cm. The average competition index of single tree decreased with the increase of diameter at breast height, and the competition pressure of diameter at breast height > 30 cm was alleviated. The competition of forests in Lin'an region mainly comes from intraspecific competition. The intraspecific competition of natural forests accounts for more than 50% of the total competition index, and the intraspecific competition of plantations accounts for more than 60% of the total competition index. The relationship between average DBH class total competition index, intraspecific competition index, interspecific competition index and diameter at breast height obeys the logarithmic function. At stand level, there are significant differences in total competition index, intraspecific competition index, and interspecific competition index among different forest types. The average total competition order was natural broad-leaved forest > natural coniferous and broad-leaved mixed forest > artificial coniferous forest > natural coniferous forest > artificial coniferous and broad-leaved mixed forest > artificial broad-leaved forest. The average intraspecific competition order was:artificial coniferous forest > natural broad-leaved forest > natural coniferous forest > natural mixed coniferous and broad-leaved forest > artificial mixed coniferous and broad-leaved forest > artificial broad-leaved forest. The average competition order among different forest types was natural coniferous and broad-leaved mixed forest > artificial coniferous and broad-leaved mixed forest > natural broad-leaved forest > natural coniferous forest > artificial coniferous forest > artificial broad-leaved forest. The average total competition index, intraspecific competition index, and interspecific competition index of artificial broad-leaved forest are the smallest. The economic tree species Carya cathayensis is the dominant tree species in this forest type, which indicates that the management measures of artificial control of low planting density effectively reduce the competition intensity of the stand in order to increase the yield of Carya cathayensis.