Abstract: The growth dynamics of grass aboveground biomass(AB) of Filifolium sibiricum grassland was studied experimentally and shown to agree with Logistic growth with maximum value, occuring in the middle of August (198.15 g·m-2 DM). After germinating the herb F. sibiricum grew quickly, the growth time needed to reach the maximum AB were less than other forbs species.There was a significant or extremily significant positive correlation between precipitation, accumulated temperature (≥5℃) and the AB increase of F. sibiricium, grass and forbs. The seasonal variation of underground biomass (UB) generally showed a “U” form, the minimum UB occurred in middle of August, the maximum UB occurred in the middle of October (1608.2g·m-2DM), and it was close to that in early spring. The net primary productivity of the aboveground part was 256.74g·m-2. year, and the underground 599.51g·m-2’. year. If the litter in growing season was included, the net aboveground primary productivity was 29.57% higher than the result estimated with maximum standing crop method.