Abstract: Based on the investigation about Castanopsis fordii of Yunzhong Mountain in Anxi, analyzed the diameter structure of stands, and researched the interspecies relationship with χ² test and relevancy degree. The results show that: The distribution about diameter class of C.fordii population is approximately 'J'-type distribution, and the distribution of ground diameter of seedling is also inverted 'J' type, while the height distribution is obvious asymmetric mountain curve, the renewal of seedlings and saplings show a growth-type structure. The χ² test of interspecies association show that the most part of the association is non-significant, and the overall trend is random. The overall competition about the population of C.fordii in study areas is not intense, and the community is in the stage of unstable development, which is easily disturbed by external factors.