In order to understand the climate and environment changes during the middle Pleistocene in the southern Xizang(Tibetan) Plateau, we studied the section located in eastern bank of Yeru River in the Dingjie Basin, southern Xizang(Tibetan) Plateau, which is lacustrine, deposited in middle Pleistocene, is consisted of a sequence of gray and white clay sand, silt, fine sand and coarse sand, with a thickness about 41. 3 m. Methods：The pollen samples are treated by hydrofluoric acid. The pollen are separated from the samples by conventional acid treatment and heavy liquid method. The age of lacustrine deposits determined by ESR and U- series dating. Results：The results show that the average pollen content of herbaceous plant, woody plant and ferns is 57. 6%, 38. 8% and 3. 5%, respectively. The vegetation types represented by pollen assemblages are grassland or forest grassland environment. According to the genus type and abundance of pollen fossils, the pollen fossils can be divided into five pollen zones from bottom to top. ESR and U- series dating data indicate that the deposition of the section is between 551. 6 and 202. 4 ka belong to the middle Pleistocene.Conclusion：The climate changes during the Middle Pleistocene in the dingjie basin are as follows: During the period of 551. 6 ~ 448. 4 ka, the climate was warm and humid, suitable for plant growth; during the period of 448. 4 ~ 375. 2 ka, the climate turned to cold and dry; during the period of 375. 2 ~ 291. 2 ka, the climate fluctuated frequently, showing a process from cold—humidity to cold—dry to cold—humidity；during the period of 291. 2 ~ 261. 0 ka, the climate turned to more dry and more cold; during the period of 261. 0 ~ 202. 4 ka, the climate fluctuated frequently, showing a process from cold—dry to warm—humidity to cold—dry.