Litter decomposition plays an important role in the carbon budget and nutrient cycling in terrestrial ecosystems, but the decomposition process and decomposition rate of litters were affected by environmental factors, especially the water condition. However, little attention has been paid to the effect of changing water condition at litter decomposition for the maize-poplar system in arid regions. Here the litters of poplar leaves and maize straws in the Hexi Corridor were selected as research objects, and there were three water treatments including normal water (9200 m³/hm², CK), mild drought stress (irrigation reduced by 15%, 7800 m³/hm²), moderate drought stress(irrigation reduced by 30%, 6400 m³/hm²), which were designed in our experiment. The mass remaining, decomposition rate and nitrogen content for poplar leaves and maize straws were measured and analyzed under different water conditions using decomposing bag method, meanwhile the effects of water changes on the decomposition characteristics of two litter types were analyzed. The results showed that:(1) the mass remaining for two litter types were increasing with increasing drought stress, but the decomposition rates were decreasing. After 164 days of decomposition, the mass remaining for poplar leaves and maize straws litter were 70.43%-77.49%, 63.55%-68.29% under three water conditions, respectively. The analysis indicated that water and time extremely significant affected the mass remaining (P<0.001), but their interactive effects on mass remaining were not significant (P>0.05). Drought stress significantly reduced the decompoation rate of maize straws, but it was only significantly decreased under moderate drought stress for poplar leaves. For the different litter types, the decomposition rate of maize straw was higher than that of poplar leaf. (2) The N remaining of two litter types was decreasing trends in the decomposition process under three water conditions, this showed that the N remaining presented releasing mode in the study period, but the N remaining was increasing with increasing drought stress, it indicated that water reducing significantly inhibited the release process of N for the two litter types. After 164 days of decomposition, the N remaining had significant difference under three water conditions for the same litter, and the decomposition time also extremely significant affected N remaining, but the two interaction has no significant effect on N remaining. For the different litter types, the N remaining for maize straws was minimum and it was maximum for poplar leaves in the same water condition, this showed the N release of poplar leaf was greater than that of maize straw. As a whole, water reducing significantly inhibited the litter decomposition and N release for the two litter types in the agroforestry system in the arid region.