Abstract: It is important that the analysis of the potential evapotranspiration and surface dry/humid index,which helps analyzing the surface water resources quantity and drought events.In the paper,the basic meteorological observation data of recent 37 years in Aershan Meteorological Bureau were used for analyzing the variations of the surface potential evapotranspiration characteristics and the humid index.The result indicated that: ① caused by the global warming influence,the annual average surface potential evapotranspiration had continuously been in an increase trend since 1980s in Aershan.② because the precipitation decreased and the potential evapotranspiration increased,the humid index had suddenly been in a decrease trend since the 21st century,the annual average humid index jump and the precipitation jump was consistent,the annual potential evapotranspiration change was consistent with the temperature change.③ the humid index analyses showed that it was driest in autumn and spring,and apt to have the drought events,the next was in summer and winter.④ from the trend analysis of the humid index(K),potential evapotranspiration(Eti),annual precipitation(R),annual mean temperature(T),the climate arid gets the aggravation tendency in Aershan,the precipitation get the concentration trend,stage arid was an aggravation and in an increase trend,thus would cause the ecological environment to have the worse trend in Aershan.

Key words: Potential evapotranspiration, Humid index, Dry/humid distributed, Characteristics jump