Globalization and elevated atmospheric Nitrogen (N) deposition have significantly altered the terrestrial carbon cycle. Soil microbial Carbon Use Efficiency (CUE) plays a key role in adjusting soil cycling rates and processes and is also an important parameter in soil C cycle models. However, the effects of elevated N deposition on soil microbial CUE are often inconsistent, which limits the reliability of predictions of both soil C cycle dynamics and C storage capacity under global changes. Here, we review advances in research on soil microbial CUE and measurement methods. We further explore the mechanisms underlying the effects of increased nitrogen deposition on CUE from both biological and abiotic perspectives in forest ecosystems. In terms of biological mechanisms, N deposition can affect CUE by changing microbial biomass and community structure and by regulating microbial enzyme activities. In terms of abiotic mechanisms, N deposition can affect CUE by changing the N addition-induced changes in the soil nitrogen state, soil stoichiometry, soil pH, and aboveground vegetation dynamics (such as root exudates and litter input), which can independently or jointly affect soil microbial CUE. In general, moderate nitrogen deposition can alleviate ecosystem nitrogen limitation and stimulate microbial activity, thus increasing soil microbial CUE. In contrast, excessive N deposition decreases microbial CUE by inhibiting microbial growth. Lastly, the potential research activities and recommendations for future research are presented. Therefore, it is imperative to optimize the determination of microbial CUE for comparative research among different ecosystems. At temporal and spatial scales, more attention should be paid to the interaction effects of multiple factors under global changes, so that there is a strong theoretical basis for evaluating and predicting the soil carbon sequestration capacity in forest ecosystems.