Abstract: The reference crop evapotranspiration（ET0）in Huaihe basin was calculated based on observed data from 171 meteorological stations from 1971 to 2010 by using of FAO Penman Monteith equation The Spatial and temporal distribution characteristics of ET0 and influencing factors were analyzed The results showed that average ET0 in Huaihe basin was 898mm and decreased at the rate of 17.5mm/10y（P<0.05）in past 40 years Most stations in northwest decreased significantly（P＜0.05）and seldom stations in southeast were increased significantly（P＜0.05）The contribution to ET0 of the meteorological factors displayed in two aspects，which including sensitivity and relative change rate of the meteorological factors The sensitivity analysis showed relative humidity was the most sensitive among the four main meteorological factors（average temperature，relative humidity，sunshine hours and wind speed），but the average wind speed changed most Wind speed had large contribution to ET0，as average temperature was little The total contribution of 4 factors to ET0 was-4.96，which meant decreased of ET0The result was beneficial to evaluate agricultural water resources and take appropriate measures

Key words: Huaihe basin, Reference crop evapotranspiration, Relative change rate, Sensitivity coefficient, Contribution rate