Abstract: By the method of fixed plots,underground structure of mixed forest of Chinese fir and Phyllostachys heterocycla cv.pubescens,which was established in 1974 by planting the pure Chinese fir forests on felled bamboo forests,was investigated.The results showed that the growth of bamboo rhizomes was atimulated by Chinese fir trees and the proportion of healthy buds increased.When the density of Chinese fir was 900～1350 trees per hectare,the proportion of healthy rhizomes root was higher,and underground structure of bamboo was optimization.There were about 92.8 percent of healthy rhizomes in the depth of 0～40cm soil layer,over 60 percent of which distributed in the depth of 0～20cm soil layer.Chinese fir trees stimulated rhizomes growing deeper.With the increase of Chinese fir density,rhizomes number in the depth of 0～20cm soil layer decreased and which in both 20～40cm and over 40?cm soil layer increased obviously.

Key words: Chinese Fir, Phyllostachys heterocycla cv. Pubescens, Mixed forest, Underground structure, Density effect