Abstract: Soil seed bank is an important indicator for plants responding to changes of the land utilization and climate，also an important tool for the understanding vegetation dynamics. In this paper，taking the Thermopsis lanceolata community in the upstream of Shiyang River，Gansu Province，China as a research object and adopting soil seed bank analysis combined with vegetation restoration determination，the soil seed banks and vegetation functional group structure，as well as their relationship are analyzed. Results show that there are fourteen vegetation species which belong to seven family. A majority of species have low dominance and the variation of dominance in vegetation community is evident. The sum of dominance of edible grass is not less than that of non-edible grass in different vegetation gradients and other non-edible grass is not able to exist stable. There are sixteen kinds of herbaceous plants in the soil seed bank of the Thermopsis lanceolata community which belong to eleven families such as composite，gramineous，leguminous and other families. The edible grass mainly belongs to composite，gramineous and leguminous family with ten total families. The density of the soil bank is 5 837±4 659 seeds·m^-2 as a percentage of 21.1%. Unedible grass mainly belongs to gramineous family in total of six kinds whose density is 21 727±14 514 seeds·m^-2 as a percentage of 78.9%. The functional group species of seeds bank presents uni-modal distribution with the variation of vegetation gradients. The number of species of edible grass seed appears descending tendency，on the contrary，the number of species of non-edible grass seed shows ascending tendency. The density of edible seed is apparently less than that of non-edible seed in different gradients. The similarity coefficient between edible grass shows reducing tendency which decreases from 0.545 in gradient I to 0.286 in gradient V. Meanwhile the similarity coefficient between inedible grass shows increasing  tendency which increases from 0 in gradient I to 0.667 in gradient V. Because of the long-term and stable existing of unedible grass in the research area，the position of excellent gramineous grass is replaced，some species of edible grass are to be eliminated and the stability，productivity and nutrient dynamics of community ecosystem will be influenced. It is impossible to recovery excellent grass in a short time if the excellent gramineous grass to be totally destroyed.

Key words: Thermopsis lanceolata community, poisonous weed containing degrade grassland, soil seed bank；functional group