Abstract: The biomass structures of Neosinocalamus affinis population and their influentive factors were studied at two levels (the population in community level and the population in individual level) using Harper′s the theory of moduler structure in Jinyun Mountain, the paper sums up the following was concluded from the result in Neosinocalamus affinis clone population the biomass distribution in the 5 age classes are 14.18%, 24.22%, 41.91%, 12.30% and 7.38%. And the current biomass of the population is 156.407t·ha-1; in the modular structure population of Neosinocalas affinis the biomass distribution per module unit of construction was 49.46% of clum, 21.34% of branch, 8.73% of leaf, 14.00% of rhizome, and 6.47% of root. In the zygote population of Neosinocalamus affinis in 200 ha, the total biomass was 31281 ton. And the proportions of above ground and the underground biomass are 79.53% and 20.47%.