The study analyzed the variation characteristics of farmland evapotranspirationin Changwu tableland from four scales: yearly, monthly, daily and growing seasonbased on observation datafrom large scale lysimeter system and explore the influencing factors by using correlation analysis and principal component analysis method. The quantitative relationship between measured evapotranspiration and influencing factors is established.The results show that the variation characteristics of farmland evapotranspiration are consistent with the growth process of the crops and the high evapotranspiration occurs in the booming period.The evapotranspiration is affected by precipitation, air temperature, wind speed, solar radiation, sunshine hours, air relative humidity and soil water content. Temperature and solar radiation are the main driving factors of evapotranspiration.