Abstract: Rainfall is limited and unevenly distributed across different seasons in the sub-humid but drought-prone area on Loess Plateau, China. Understanding the effects of water supply on the growth of forage crops is of great significance for guiding forage cultivation. Pot experiment was carried out in a shelter in this study. There were five cropping patterns, including monoculture of common vetch, oat and maize, oat/common vetch intercropping, and oat/maize intercropping. There were three water supply levels, including high (low limit of 70% field capacity), medium (low limit of 55% of field capacity) and low (low limit of 40% of field capacity) water. The results showed that land equivalent ratio in the oat/common vetch intercropping group were 1.20, 1.21 and 1.19 at the high, medium and low water supply levels, respectively, and those in the oat/maize intercropping were 1.17, 1.11 and 1.03. Such results indicate that all of the intercropping systems had yield advantages compared with all monoculture. Among the five planting patterns under the same water supply level, the total dry matter yield of maize monoculture was the highest, and that of common vetch monoculture was the lowest. Yields of dry matter and crude protein of oat increased with the decreases of water supply, while common vetch and corn monoculture showed opposite trends. On per plant basis, intercropping increased dry matter yield and crude protein yield of oat, while decreased the yield of common vetch and maize, oat showed an intercropping advantage. Compared with the high water treatment, dry matter yield of the oat/common vetch intercropping increased insignificantly by 4.1% and 4.8% respectively compared with that in the treatments of medium water and low water, whereas dry matter yield of the oat/maize intercropping was significantly reduced by 8.0% and 13.0% respectively. Compared with high water treatment, root/shoot ratio of the oat/common vetch intercropping was significantly increased by 33.4% and 58.4% under the treatments of medium and low water respectively. However, medium and low water supply significantly reduced root/shoot ratio in the oat/maize intercropping. Compared with high water treatment, water use efficiency of the oat/common vetch intercropping significantly increased by 11.7% and 12.9% under the treatments of medium and low water respectively, while water use efficiency of oat/maize intercropping was not affected by water application. In summary, yield of forage maize monoculture and oat/forage maize intercropping were higher, but they were sensitive to water shortage and had low yield stability. Under insufficient water conditions, yield stability, crude protein production and water use efficiency in oat/common vetch intercropping system were greater. Consequently, we suggest this system should be used in the study area.