Abstract:The biomass dynamics of Cryptomeria japonica (L．F)D．Don was studied by the use of Richards model·The stand biomass (W，t/hm2)can be calculated by the followingfunctions， W=318．0349 (1-e-O．1414sst)1/1-0.664835，where t is the sand age in years． The result showed that the growth process of Cryptomeria japonica to 16 years can be divided into three stages：1 to 5—year is young growth stage：5—10th year is pole stage；after 10th year will be submature stage．The calculating result is that the maxi-mum biomass will amount to 318．Ot/hm2．