The water-saving society construction is a basic policy in China and a strategic choice to obtain the sustainable use of water resources in the arid lands. The Weigan River basin is a typical irrigation farming region in the arid lands, the majority of agriculture irrigation is extensive, such as earth canal and flooding irrigation. The water loss is serious, irrigation quota is high, canal infiltration is more than 1.4 billion m3, and the water-saving potential of agriculture irrigation is large in the Weigan River basin. On the condition of no increase of water quantity in the near future, adjusting the agriculture internal planting structure and developing water-saving agriculture is a favorable measure to solve water shortage problems. In this paper, the determination of the amount of water-using in agriculture irrigation based on a prediction of industry, urbanization and ecological water requirement was made. We selected nine kinds of crops with large acreage, took the amount of evaporate-transpiration and planting index of these crops as reference factors to conclude the actual amount of water-consuming of the crops. Compared with the current irrigation amount, we found that the current irrigation amount was greatly larger than the actual demand of the crops. We might save water more than 108 m3 by water-saving irrigation and water channel improvement. The actual grain planting area of the study region is out of the scale in need. Even if we will not expand the grain planting area any more in the next decade, there still exists nearly 20 000 hm2 beyond the minimum needed area. If we adjust the planting area according to actual demand, we may save neraly 100 million m3 water. It can greatly ease the water shortage and control the irrigation amount in a range of available water. Meanwhile, it can also provide plenty of water resource for ecological protection, urbanization and industrialization.