Litter decomposition is an important ecological process which links the ground and underground components of an ecosystem, and determines the rates of nutrient cycling. However, it is still not clear that how litter decomposition is affected by grazing and potential increase in water and nitrogen (N) availability, especially in the desert grassland ecosystems where decomposition is relatively slow. In this study, we conducted an experiment on litter decomposition in a desert steppe dominated by Stipa breviflora with previous influences under different grazing intensities (no grazing, light grazing, moderate grazing, and heavy grazing) in combination with N addition (0.0 or 10.0 g N m^-2 a^-1) and water supplementation (0.0 or 108.0 mm/a). Our results showed that both grazing intensity (P<0.0001) and N addition (P<0.05) had significant effects on litter decomposition. After a short period decomposition (135 days), there was a significantly negative correlation between the initial litter C:N ratio and the constant of litter decomposition rate, indicating that litter quality played an important role in this short-term decomposition. Litter decomposition was fastest under light grazing intensity as a result of significantly lower litter C:N ratio than those of other grazing intensities. This indicated that grazing with appropriate intensity was not only beneficial to community maintenance, but also favorable to cycling of nutrients in grassland ecosystems. After a long period of decomposition (870 days), the decomposition rates in the non-grazing plots were significantly lower than those in the grazing plots regardless of grazing intensity. In addition, the decomposition was not influenced by the initial litter quality (C:N ratio), rather it was positively correlated with the diversity of soil microbes, and negatively correlated with the community coverage. Nitrogen addition had no significant effects on litter N content, but slowed down the decomposition significantly. We also found that adding water in growing season did not affect litter quality and litter decomposition rate. Our results implicate that short-term litter decomposition was controlled by the initial litter quality while the long-term litter decomposition was influenced by solar radiation in the studied steppe ecosystem.