Abstract: In this paper, we analyzed water uptake and water use of plant under different intercroppings, probed the mechanism that intercropping can increase yield, propounded optimal intercropping model that suited for the local ecological environment, and provided some theoretical basis. Field experiments were carried out from 2009 to 2010 in Wuchuang, Inner Mongolia, and water uptake and water use under different potato/sunflower intercroppings was studied. Results showed that the two potato/sunflower intercrops had yield advantage. The land equivalent ratios (LER) of two rows potato and 2 rows sunflower (2P:2S) and four rows potato and four rows sunflower (4P:4S) intercropping systems ranged from 1.2 to 1.3. That for 4P:2S was highest (1.26), had a significant advantage in land productivity. The actual evapotranspiration (ET) of potato between intercropping and sole systems was not significantly different. The same results were existed for sunflower. Comparison with water use efficiency (WUE) of sole potato, although the WUE of intercropped potato in 2P:2S intercrop and 4P:4S intercrop decreased 81% and 66%, but the WUEs of intercropped sunflower in two intercrops were as the same as that of the monoculture, therefore, the WUEs of the intercropping systems at field level were increased. Water use equivalent ratios (WER) of two intercrops ranged from 1.2 to 1.3, especially, in 4P:4S intercropping system were 1.3, indicated that this intercropping system had highest advantage in water use. It is concluded that the potato/sunflower intercrops, especially for 4P:4S intercrop, improve the land productivity and water use efficiency, and could be applied in sustainable development in the region of rainfed agricutlure.