An integrated simulation model for inter-basin water transfer and allocation, WatM-IITA, is developed,to systematically consider the dynamic feedback between processes of natural water cycle and human water use, and to simulate the distributed inter-basin water transfer and allocation and transformation processes of the water cycle under their influence.Taking the Yintao Water Transfer Project in Gansu Province as an example, the effects of inter-basin water transfer on the water supply structure and the volume of water resources are assessed across spatiotemporal scales under different typical annual climatic conditions. The results indicate that inter-basin water transfer effectively enhances domestic and industrial water supply security in the water-receiving area. In severe drought years, the domestic, industrial, and irrigation water shortage rates decrease by 15.9%, 19.1%, and 34.3%, respectively. Regions with higher water demand but poorer natural water resource endowment and greater climate sensitivity show more constrained water shortage alleviation. Inter-basin water transfer significantly increases the volume of surface water resources in the water-receiving area, particularly in regions with substantial irrigation supplementation, while its impact on the volume of groundwater resources and its spatiotemporal distribution patterns remained marginal. In severe drought years, the volume of surface water resources increases by 84 million cubic meters.