The source area of the Yellow River (33°-36°N. 95°-100°E. and higher than 430, on an average) is located in the east part of Qinghai-Xizang Plateau. Widespread glacial relics.such as streamlined landforms including roches moutonnees and whale back. glaciated troughs. smoothed hill tops, till deposits. qranodiorite erratics stria stones. kame deposits and so on. indicate that there was an ice sheet in this region during Pleistoene. The ice sheet covered an area of about 80000km² and the centred of it is near the peak of Bayan Har mountain. south of which is the Changjiang drainage basin. Calculating by the equations H=3. 4L^1/2and logv=1.23 (logs-1) (where H is thickness of centre of ice sheet. L is radius. V is ice volume and S is area). the thickness of the centre and the ice volume of the ice sheet were up to about 1360m and 63000km³ respectivily. We cna deduce that the glacier began to develop around the mountains and gradually covered all the area.The snowline of the modern glaciers on the Anyemagen Mountain, situated in the east of the area. lies at 5090m. and it was 4600m high during last glaciation and 4300m high during Penultimate ice age in the Ela Mountain, which is situated in northeast of the area. So we think that the ice sheet was developed not later than penultimate ice age when the plateau surface was much lower than that of today. and the snowline at that time was also lower than 4300m, Climatic data shows that. at present. the temperature is the lowest and the precipitation is relatively abundant in this area in the Qinghai-Xizng Plateau because of the influence of the monsoon. This is probably the reason why the ice sheet was formed only in this area but not in the west part of the plateau where the land surface is much higher. Some ice wedges developed at 135. 7±10.5 kaB. P. were found near Xinghai County (350m).which indicate that the mean annual temperature was approximately 10℃ lower than today.This Pleistocence ice sheet was the largest one found so far at present in the Qinghai Xizang Plateau.