Soil microbial community composition and litter quality are important drivers of litter decomposition, but how litter quality influences the soil microbial composition largely remains unknown. We conducted a microcosm experiment to examine the effects of changes in litter quality induced by long-term N deposition on soil microbial community composition. Mixed-species litter and single-species litter were collected from a field experiment with replicate plots exposed to long-term N-addition in a semiarid grassland in northern China. The litters were decomposed in a standard live soil after which the composition of the microbial community was determined by Illumina MiSeq Sequencing. Changes in litter stoichiometry induced by N-addition increased the diversity of the fungal community. The alpha-diversity of the fungal community was more sensitive to the type of litter (mixed- or single-species) than to the N-addition effects, with higher abundance of fungal OTUs and Shannon-diversity observed in soil with mixed-species litter. Moreover, the relative abundance of saprophytic fungi increased with increasing N-addition rates, which suggests that fungi play an important role in the initial stages of the decomposition process. Litter type and N addition did not significantly change the diversity of bacterial community. The relative abundance of ammonia-oxidizing bacteria was lower in high N-addition treatments than in those with lower N input, indicating that changes in litter stoichiometry could change ecosystem functioning via its effects on bacteria. Our results presented robust evidence for the plant-mediated pathways through which N-deposition affects the soil microbial community and biogeochemical cycling.