Although the level of nitrogen (N) deposition in China has gradually stabilized in recent years, N deposition in Southeast China is still at a high level compared to other regions. The effect of N deposition on the carbon cycle of terrestrial ecosystems cannot be ignored. Microbial carbon utilization efficiency (CUE) refers to the efficiency of microorganisms in converting absorbed carbon into biomass carbon; high microbial CUE implies high soil organic carbon storage potential, while low microbial CUE implies high carbon loss from the soil. High microbial CUE means high soil organic carbon storage potential. Therefore, exploring the changes of microbial CUE under the N deposition will help to further understand the changes of soil carbon storage in terrestrial ecosystems. However, there are few reports about how the change of microbial community structure affects microbial CUE under N deposition. In this study, N deposition was simulated by N addition in Castanopsis fabri forest in Daiyunshan National Nature Reserve, Quanzhou City, Fujian Province. The experiment included three N addition treatments: control (CT, +0 kg hm^-2 a^-1), low nitrogen (LN, +40 kg hm^-2 a^-1), and high nitrogen (HN, +80 kg hm^-2 a^-1). The soil physical and chemical properties, microbial biomass, enzyme activity, and CUE of different treatments were determined. The microbial community structure and diversity were determined using high-throughput sequencing. The results showed that the N addition significantly affected microbial CUE, which gradually increased with the increase of N addition. On the contrary, soil pH, extractable organic carbon (EOC), and microbial biomass carbon (MBC) showed a downward trend. There was no significant effect of N addition on soil microbial community α-diversity. Non-metric multidimensional scale (NMDS) analysis showed that N addition significantly changed the microbial community structure. Especially for fungi, the fungal communities with different N addition treatments were obviously divided into three clusters. Microbial CUE was negatively correlated with soil pH, EOC, and fungal NMDS1, and positively correlated with mineral nitrogen. Random forest analyses showed that the taxa affecting microbial CUE under N addition were predominantly eutrophic (e.g., Ascomycetes and Ascomycetes) and were able to devote more carbon to growth than respiration compared to nutrient-poor taxa. To sum up, this study shows that microbial CUE is not only regulated by soil nutrient availability and pH, but also affected by soil microbial community structure under N addition. Therefore, further exploration of changes in key soil microbial taxa under N addition in the future may help to reveal the carbon storage process in forest ecosystems.