The high-intensity utilization of global cropland causes water shortage and food crisis, which seriously affects the re-alization of SDG 2 (zero hunger), SDG 6 (clean water and sanitation) and SDG 15 (life on land), and threatens the sus-tainable social, economic and ecological development. Cropland fallow can not only improve the quality of cropland and maintain ecosystem balance, but also have a significant water-saving effect. However, in most developing coun-tries, such as China, cropland fallow has not yet been widely promoted, and there are few reliable fallow cropland fallow identification methods, making it even more challenging to assess the water-saving effect. To remedy this def-icit, we propose a framework for mapping cropland fallow and evaluating its water savings. First, we used the Landsat series of data to interpret the annual land use/cover changes in Gansu Province, China from 1991 to 2020. Subse-quently, the spatial-temporal variation of cropland fallow in Gansu province (giving up farming for one to two years) was mapped. Finally, we evaluated the water-saving effect of cropland fallow using evapotranspiration, precip-itation, irrigation maps, and crop-related data, instead of actual water consumption. The results showed that the map-ping accuracy of fallow land in Gansu Province was 79.50 %, which was higher than that of most known fallow mapping studies. From 1993 to 2018, the average annual fallow rate in Gansu Province, China, was 10.86 %, which was ata low level in arid/semi-arid regions worldwide. More importantly, from 2003 to 2018, cropland fallow reduces annual water consumption of 303.26 million tons in Gansu Province, accounting for 3.44 % of agricultural water use in Gansu Province and equivalent to the annual water demand of 655,000 people in Gansu Province. Based on our re-search, we speculate that the increasing pilot projects of cropland fallow in China can bring significant water-saving effects and help achieve China's Sustainable Development Goals.