Climate change has a great impact on hydrological cycle and water resource management in catchments. Under standing the change in reference evapotranspiration (ET_0) in a catchment can improve its water resource management. In this paper, the change of ET_0 in Fenhe Irrigation District and the factors affecting it were analyzed using long-term climatic data in this region. The results showed that the annual ET_0 in Fenhe Irrigation District did not show a significant (P>0.05) change from 1951 to 2014, because the positive effect of the increased temperature and decreased relative humidity on ET_0 was compensated for by the negative effect due to the decreased wind speed and sunshine time. Changes in temperature, relative humidity and wind speed affected ET_0 considerably from April to June, while sunshine hours impacted ET_0 from May to September. Our results can help to efficiently allocate water resources in Fenhe Irrigation District as well asin the Fen River basin.