Abstract: This paper briefly describes the main characteristics of physical geographic conditions in the riverhead area of the Yangtze River, in the Qinghai-Xizang Plateau, and deals with the influences of glaciers,cryopedolcgical conditions and geological structures upon stream systems and river regimens.Some regularities of variations of runoff, flood, low water, water temperature and river freeze are involved in the paper.The basic features of flood generation can be analyzed on the basis of relevant physical geographic conditions in the area. According to observation data and flood investigations, an estimation of flood peak discharge with 100 year recurrences of the rivers in the area is presented for designing the railway and highway bridges.