The Dingjie section is located in Eastern bank of the Yairu Zangbo(River) in the Dingjie Basin, Xizang(Tibet). ESR dating shows that the lacustrine deposit is Middle Pleistocene in age. The sediments exposed here are 41. 3 m thick,which consists of a sequence of gray /gray - white clay sand,silt,fine sand and coarse sand. Abundant ostracods,including 10 genera and 26 species,are found here. Based on the ostracods type and abundance changes,the environment,lakes and climate envolution of the Dingjie Basin during the Middle Pleistocene is divided into the following 6 phases: (1) Period 1 (543. 8 ~ 437. 9 kaBP),during this period, climate of the lake area was cool and wet. The lake surface is wide with a little salinity and the temperature of the lake water is low. (2) Period 2 (437. 9 ~ 34. 77 kaBP),the climate became colder than Period 1. The water level of the lake may become lower,and the lake developed into more salinity. (3) Period 3 (34. 77 ~ 264. 2 kaBP), climate became colder and colder. At the same time,the water level became higher than the last period. The salineness of the lake water reduced with desalinate development. (4) Period 4 (264. 2 ~ 254. 9 kaBP),the temperature of lake water continued to decline,and the water level gradually increased after shrink in the last stage. (5) Period 5 (254. 9 ~ 239. 0 kaBP),the water level of the lake decreased and climate became warmer. (6) Period 6 (239. 0 ~ 184. 0 kaBP),the lake expanded than the previous period and desalinated obviously,but climate was still cold.