In recent years, the rate of atmospheric nitrogen (N) deposition in China has been increasing. Excessive N input has a strong impact on the carbon (C) cycle of terrestrial ecosystems in China. Although a large number of studies have reported the effects of simulated N deposition experiments on the C dynamics in terrestrial ecosystems in China, due to the complex geographical conditions and different fertilization regimes, the general response and the mechanism of plant and soil C pools to N addition are still widely debated. Here, we collected and compiled the available data from 172 published field N-addition experiments in China to assess the effects of N addition on plant and soil C dynamics in terrestrial ecosystems by meta-analysis, and to explore its underlying mechanism at the national scale. The results showed that N addition stimulated plant C fixation, both aboveground and belowground biomass were significantly increased, and the response of aboveground biomass was higher than that of belowground biomass. Meanwhile, N addition significantly increased litter mass, but it did not significantly affect fine root biomass. The ratios of C:N in plant leaf, litter, and fine root were significantly decreased by N addition. Generally, N addition increased soil organic C (SOC) concentration and decreased soil pH across all the selected studies, while it had minor effects on dissolved organic C (DOC), microbial biomass C (MBC), and soil respiration (SR). We found that the responses of SOC concentration to N addition were increased, decreased, or unchanged under different geographical variation. Regression analysis showed that there were negative correlations between aboveground biomass vs. SOC, and MBC vs. SOC. Despite N addition significantly increased plant C inputs into the soil via increased litter mass, it also might increase the soil C decomposition by stimulating microbial degradation, since elevated N input would provide high-quality substrates via significantly decreasing the C:N ratio in litter and fine root. The response of SOC accumulation to N addition depends on the trade-off between plant C input and soil C output. In conclusion, we suggest that N addition increases plant C sequestration and soil C storage in terrestrial ecosystems in China, and the effect magnitude was dependent on the ecosystem types and fertilization regimes. Our findings highlight that the negative correlation between aboveground C input and SOC under N deposition may affect the prediction of terrestrial soil C budget, and this relationship should be given full consideration in further ecosystem models.