Abstract:The development of understory in the Chinese fir stand in the Dagangshan, and the law of its biomass accumulation and allocation have been discussed in this paper. The relations of understory, the growth of Chinese fir trees, and site types have been expounded. The results indicate that understory develops quickly and its biomass could accumulate 4—5 t/ha in 4—5years. Therefore, it provides the scientific basis for further investigating how to use the understory and conserve and increase the Chinese fir forestland capablity.