Based on the data of air temperature,precipitation and evaporation at 16 meteorological stations in the headwater of the three-river-area from 1962 to 2001,the abnormal character of climate changes in recent 40 years and its effect on ecological environment are analyzed. The results show that air temperature appears to be an increasing tendency,precipitation is reducing and evaporation is increasing in the region. At the same time,arid climate and artificial activity leads to the hungriness of ecological environment,such as degenerating of the pastures,shrinking of the lakes,decrement of flow curve,deserting and losing of water and soil etc.