Abstract: Not only the distribution range of the Spodiopogon sibiricus community on woodland of the loess plateau in north Shanxi Province is widespread, its quality is also excellent. It occupies a very important position in animal husbandry. We have investigated the seasonal and spacial variation of both aboveground part and underground biomass in Spodiopogon sibiricus community. The result indicates that: the biomass seasonal dynamics was evident, the biomass of aboveground achieved peak value (243.1g/m2) in the midmonth of September; the biomass of underground was medium during the reviving period, minimum during flourishing period, maximum during the withering period. The observed facts are related to the stages and organic matter transport.