Simulating and estimating the influence of climate change on spatiotemporal characteristics of reference evapotranspiration(ET_0) provides support for developing water-saving agriculture and efficient use of water resources. The Penman-Monteith equation is employed to calculate daily ET_0 for the 11 meteorological stations located in and around the Shiyang River basin during 19512012. While ET_0 in 2020s,2050s and 2080s are downscaled from HadCM3 (Hadley centre Coupled Model,version 3) outputs under A2 and B2 emission scenarios by SDSM (Statistical Downscaling Model). The spatial distribution and temporal trend in ET_0 are investigated by Inverse Distance Weighted Interpolation and Mann-Kendall test,respectively. The results show that the annual mean ET_0 in the Shiyang River basin is 1 061mm,the highest values are located in the northeast region,and the lowest values are located in the southwest region. HadCM3 projects an ET_0 increase of 6%,14%,23% under A2 scenario in the 2020s,2050s and 2080s,respectively,while it projects an ET_0 increase of 7%,12%,17% under B2 scenario,an obvious amplification is detected in the southeast region,in 2050s and 2080s,the ET_0 increase under B2 scenario are lower than those under A2 scenario. It will be a significant ET_0 increasing trend in the future and after the 2050s.