Based on the data of evaporation, temperature, precipitation, sunshine duration, vapor pressure from 4 meteorological stations in Huangnan of Qinghai Province in the recent 54 years, using the data from the geographic information system, by means of the methods of mathematical statistics, linear regression and MannKendall test, the trends of spatial and temporal variation of evaporation in Huangnan are studied, and the characteristics of evaporation variation and the influencing factors are analyzed. The results indicated: (1) The average annual evaporation in Huangnan was 1441.5 mm from 1961 to 2013, which showed an obvious decreasing trend. In the 1960s and 1970s, the evaporation capacity had an increasing tendency. From the 1980s, the evaporation capacity decreased, presenting a declining trend. (2) The evaporation was the greatest in spring and summer, accounting for over 60 percent of average annual capacity, and it was less in autumn and winter. Evaporation capacity saw a decreasing trend in all seasons, especially in spring, then in summer. (3) In 1973, Huangnan experienced a sudden change in annual evaporation from great to low, and seasonal sudden change from great to low happened in the spring of 1973, summer of 1975, autumn of 1976, and winter of 1974, respectively. (4) The analysis of the influencing factors of evaporation shows that evaporation had a significant positive correlation with sunshine and a negative correlation with vapor pressure. The reduction of sunshine duration was the main influencing factor of evaporation decrease.