Agricultural water-saving studies based on remote sensing evapotranspiration (RS ET) data are beneficial supplements to traditional agricultural water-saving studies. Crop water production function based on remote sensing ET data was built with classification mean value method. As far as lower crop water consumption and higher water productivity were concerned, crop ET quota model for water resource vulnerability region was put forward. The ET quotas of winter wheat and summer maize were calculated as 346 and 313 mm, respectively, by using the ET quota model. Based on the structure of current land use, water-saving potential under ET quota management was determined by adjusting the values of pixel based on the selected ET quotas of crops as evaluation criteria. The water-saving potentialities of summer maize and winter wheat in Daxing District were 176.75 and 369.27 ten thousand m3. The research provides a beneficial exploration on quantitative evaluation of regional water-saving and water consumption potentialities by using remote sensing evapotranspiration data.