Abstract: The Yourdusi basin is a high-elevated intermontane basin on the southern slope of the Tianshan Mountains,it is divided into large one and small one by a mountain,and the latter is located on the north side.The small Yourdusi basin is 2500~2700m a.s.l.,its sedimentary material is mainly composed of alluvial,diluvial,fluvial and lacustrine deposits,and its marginal ring-shaped belt is covered by diluvial deposits.The annual temperature,the lowest one in January and the highest one in July are -4.8℃， -46.6℃ and 28℃,and the annual precipitation and evaporation are 264 and 1022~1247mm respectively.Swamp meadow and swamp vegetation distribute extensively.Based on analysis on the Holocene sporo-pollen samples,the evolution of the paleovegetation and paleoclimate is discussed in the paper. Through analyzing,the following conclusions can be obtained：
（1）Modern climate in the basin is dry and cold,and there are no forests in the surrounding mountains.Whereas the pollen content of China fir is as high as 27.8% in the surface deposits, which shows that the surface deposits are not the modern ones,and the spore-pollen composition of the upper zone IV represents a relative humid-cold climatic fluctuation in the late Holocene（about 1500 a B.P.）through comparing it with that in the Bosten Lake section downstream,Altay Daluoba Section in north Xinjiang,and barkol Lake section in east Xinjiang;and the lower deposits formed in the early Holocene（about 9000~8000 a B.P.） according to the environmental evolution sequence reflected by the data of ¹⁴C dating,lithology,sedimentary speed and spore-pollen spectrum.
（2）From a view point of the spore-pollen composition,climate in Holocen here was slightly humider than that at present,and the meadow grassland vegetation ever distributed in the basin grows on the sheltered-slope of the mountains of 2700~2900m a.s.l.
（3）The pollen of the main plants in the community,wormwood artemisia and bryophyte,is difficult to distinguish under a microscope.
（4）The high pollen content of pine family in zone IV does not represent the underforestal deposits,and is possibly a surperposing result of wind and fluvial actions.

Key words: spore-pollen, vegetation community, environmental evolution, Yourdusi basin．