Abstract: Based on the general meteorological data recorded by 14 stations from 1964 to 2013 in the Three-River Source Area, the spatial and temporal variation and trend of evaporation were analyzed using linear trend estimation and Mann-Kendall abrupt change test, and the causes of increasing evaporation were analyzed by the full correlation analysis. The results showed that the annual evaporation was increasing significantly in Three-River Source Area, and the linear change rate was 30.1 mm/10 a. The change of evaporation in summer, fall and winter was significant. The evaporation in summer and fall contributed to annual evaporation mainly. The monthly evaporation was generally increasing, but the rate different. The winter evaporation was changing abruptly in 2011. The other seasons and annual changing were not abrupt. The monthly evaporation was not significant, distributing double peaks, and peaks appeared in May and July, the minimum was in January. Seasonal change was obvious. The max evaporation was present in summer, secondly in spring and fall, minimum in winter. That showed evaporation in spring and summer played an important role on hydrologic cycle in Three-River Source Area. Annual and seasonal evaporation showed the northwest was less, the southeast and northeast was more. Climate change rate increased from west to east. The change of annual evaporation was not acute, the rates were increasing from northwest to southeast. The rates of seasonal evaporation distributed differently in space. Annual evaporation was positively correlated with average temperature, but had negative correlations with daily range of temperature and relative humidity. The main reasons of evaporation decline are the rise of average temperature, and the decline of daily range of temperature and relative humidity.

Key words: evaporation over evaporating basin, average temperature, relative humidity, daily range of temperature