The study of crop water requirements (CWR) under climate change is critical for reasonable crop irrigation. In the present study, the effects of changes in climatic variables from 1961 to 2010 on maize CWR in Huang–Huai–Hai (HHH) watersheds in China were investigated. Five daily climatic factors including maximum temperature (Tmax), minimum temperature (Tmin), wind speed (u2), sunshine hours (nsun), and relative humidity (RH) from 121 weather stations during the maize growing season were studied. The Penman–Monteith method was employed to calculate crop evapotranspiration (ETc), and the spatiotemporal distribution characteristics of ETc and climatic factors were investigated via singular value decomposition. Results showed that the ETc of spring maize slightly increased by 0.4% during the past 50 years, which was primarily caused by the increase in Tmax. The ETc of summer maize decreased by 10.5%, which was primarily caused by the decrease in nsun and u2. Overall, the ETc followed the same spatiotemporal change trend as those of Tmax, nsun, and u2 in the HHH, whereas no coexisting spatiotemporal change between ETc and RH, as well as Tmin, was observed. This result suggests that changes in Tmax, nsun, and u2 are the main climatic factors that influence maize CWR in the HHH.