Abstract: The paper aims to study the variation characteristics and influence factors of reference evapotranspiration in Xianyang. Daily reference evapotranspiration (ET0) during 1981-2012 was calculated by using Penman-Monteith equation, based on daily meteorological data of Xianyang, the variation of ET0 and main meteorological factors were analyzed, the sensitivity of daily ET0 to main climate factors, such as temperature, sunshine hours, average wind speed and average relative humidity was analyzed by using the methods of response curves and sensitivity matrix. The results showed that: (1) the annual average daily ET0 in Xianyang was steady as a whole which was 2.37 mm/d, fluctuations were in a range of 0.3 mm/d; (2) the annual average temperature, the maximum temperature and the minimum temperature in Xianyang generally showed a significant increasing trend, while the average wind speed and average relative humidity decreased; (3) the inter-annual and seasonal variation of average daily ET0 during 1981-2012 in Xianyang was not obvious; (4) the daily ET0 was in positive relation with temperature, sunshine hours and average wind speed and in negative relation with average air pressure and average relative humanity, and average relative humidity was the most sensitive to ET0 in Xianyang. The results can provide certain guidance for determining local crop water requirement.