Nitrogen (N) deposition and precipitation change are important phenomena in global climate change and they can strongly influence grassland ecology. There have been many studies on the response of plant and soil microbial communities to N addition. However, the interactive effects of N addition and irrigation on soil microbial communities are still largely unknown. Studying the effects of nitrogen (N) deposition and precipitation change on soil microbial community structure is of great significance for predicting the interactive effects of multiple climate factors on grassland ecosystems in the future. Here, we simulated N deposition and precipitation change by N addition (0, 15, 30, 50, 100, 150, 200, 300 kg N hm^-2a^-1) and irrigation (no irrigation and irrigation equivalent to 100 mm extra summer rainfall) at a test area on the Stipa baicalensis steppe. A split-plot design was adopted. Soil samples were collected with a soil probe after four years of experimental treatments. Using high-throughput sequencing technology, we evaluated the interactive effects of N addition and irrigation on the soil bacterial community structures. Statistical analyses showed that N addition and irrigation significantly (P < 0.05) shifted the composition and relative abundance of the soil bacterial community.The dominant bacterial phyla were Verrucomicrobia (30.61%-48.51%), Proteobacteria (21.37%-29.97%), Acidobacteria (9.54%-20.67%), and Bacteroidetes (4.96%-9.74%). Under normal precipitation, the relative abundance of Verrucomicrobia significantly decreased in N100-N300 (P < 0.05), but the relative abundance of Proteobacteria, Acidobacteria, Actinobacteria and Bacteroidetes increased with high N addition levels. However, the relative abundance of Firmicutes did not significantly change. When water was added with N, the relative abundance of Verrucomicrobia increased following the increase of N addition rates and significantly increased in N200-N300, but the relative abundance of Acidobacteria, Firmicutes and Actinobacteria decreased after N addition. The relative abundance of Proteobacteria and Bacteroidetes did not significantly change under N addition combined with irrigation. The ANOVA of the split-plot design showed that N addition and irrigation interactively affected the structure of the soil bacterial community. The results of the Linear Discriminant Analysis (LDA) showed that the relative abundance of 19 bacterial phyla significantly shifted under different N and water addition rates. The changes in soil bacterial community structure were mainly related to changes in the relative abundance of the phyla Verrucomicrobia and Acidobacteria. Hence, phyla Verrucomicrobia and Acidobacteria could be used as indicator species for changes in soil bacterial community structure. In all, N addition and irrigation significantly changed the structure of the soil bacterial community. N and water addition interactively affected the relative abundance of different soil bacterial phyla.