Abstract: By conducting field investigation of the herbaceous community characteristics in lower reaches of the Tarim River and combined with the groundwater depth data, this paper discussed the relationship between groundwater depth and characteristics of herbaceous. The results revealed that: (1)with the increase of groundwater depth, the biodiversity and coverage of herbaceous presented a decreasing trend, and the ecological structure tended to be simple; The composition and species diversity of herbaceous were relatively high where the groundwater depth shallower than 6 m, while, fewer herbaceous plant distributed where the groundwater depth deeper than 7 m. (2)At large scale space, the distributed characteristics of herbaceous along with groundwater depth was in agreement with other desert region, i.e. as the groundwater depth increased, the order of succession was Phragmites Adans community with high water level, Glossogyne tenuifolia community with medium water level, Alhagi sparsif community with lower water level; there were otherness, similarity, and continuity among the herbaceous community corresponding to different groundwater depth. (3)The ecological niche width of advantage herbaceous species was not wide in the lower reaches of Tarim River, due to the restriction of water environmental conditions; while the ecological niche width of Phragmites communis and Alhagi sparsif, which were widely distributed, wider than others. To sum up, groundwater depth was the key factor which affected the species composition and type of herbaceous.

Key words: dominant herbaceous species, groundwater depth, similarity coefficient, ecological niche width, Tarim River