The disparity in unit irrigation water consumption (UIWC) of different cropping systems provides an opportunity to reduce total irrigation water consumption (TIWC) by optimizing cropping systems. However, the UIWC for diverse cropping systems has neither been systematically quantified nor been optimized at a national scale. Here, we quantify the cropping system-specific UIWC and TIWC for the major cropping systems in China during 2014-2018 and estimate the potential of TIWC reduction by optimizing the cultivated areas of 17 cropping systems in each prefecture. The TIWC is about 154.1 km³ yr⁻¹ for Chinese cropping systems, mainly including single rice (25.8%), early-late rice (16.6%), winter wheat-summer maize (13.9%), single spring maize (12.5%) and cotton (9.4%). Optimizing cropping systems by increasing the cultivation areas of winter wheat-summer maize, spring rape, single summer maize, single spring maize and cotton, in the meantime reducing those for single winter wheat, single rice and soybean, can reduce the TIWC by 5.3% ±1.6% in China and by more than 10% in 23.9% of the prefectures, especially in the North China Plain and Southwest China. The water-saving potential is highly influenced by irrigation water availability and minimum crop production limitation. Our findings provide a novel framework to optimize cropping systems and minimize TIWC without compromising food security and economic benefit, which can accelerate realization of water-saving agriculture.