Estimating reference evapotranspiration (RET) under the future climate scenarios,and further revealing the hydrological response to the future climate change,are helpful to provide scientific and theoretical basis for water resources planning and management. In this study,RET was calculated using FAO Penman-Monteith method during the period 1961-2010 according to the daily meteorological data of 40 stations across the Haihe River Basin. The projected daily RET of HadCM3 under A2 (H3A2) and B2 (H3B2) scenarios were downscaled to local meteorological stations using the statistical downscaling model (SDSM). Spatial and temporal patterns of RET in the future (20112099) were analyzed. The results show that, the SDSM model performs well in simulating RET in the Haihe River Basin. Although the RET of most stations declined during the past 50 years, projected future RET in most areas would increased, especially in the northwestern edge of the area,Luanhe River upstream and downstream,and Tuhaimajiahe River Basin. The increase amount of RET under H3A2 would be slightly higher than that under H3B2. The decrease of RET could mainly be expected in the central basin in 2020s, with gradually shrinking to the Jing-Jin-Tang region. Furthermore, spatial and temporal heterogeneities could be found in changes in seasonal RET. Seasonal RET would increase in most regions of the Haihe River Basin, except spring RET in the southern river basin, the autumn RET in Luanhe River downstream and northeastern of the Haihe River Basin,and the winter RET in the southwest and northeast of the basin. Meanwhile, the future increasing temperature should be mainly responsible for the increasing RET on the whole basin.