Abstract: The characteristics of water balance over Yalu Tsangpo River basin in Tibet are researched by using NCEP/NCAR twice daily (0000 and 1200UTC) reanalysis data,monthly runoff and precipitation for the period of 1980-1989,and the evaporation,soil and surface water storage are also estimated.The main results are as follows:(1) the Yalu Tsangpo River basin acts as a risture sink from May through October,where precipitation exceeds evaporation,and as a moisture source during NovemberApril,where evaporation exceeds precipitation;(2) in Yalu Tsangpo River basin,precipitation mainly occurs during summer,and runoff,whose peak value lags that of precipitation one month,cheifly supplied by precipitation;(3) the soil and subsurface water storage decreases from January to June,but increases after July and reaches its maximum in October;and (4) over Yalu Tsangpo River basin there are raising trends in precipitation,evaporation,and runoff in late 1980s,which are related to ENSO events.