Abstract: In order to explore the long-term effects of different proportions of organic carbon input on nitrogen supply capacity of tobacco-planting soil under fertilizer reduction, four treatments were set up based on 11 consecutive years of field location experiments: no fertilizer (CK), local conventional recommended fertilizer (100% fertilizer, CF), 20% chemical fertilizer reduction with 3000 kg·hm^-2 organic fertilizer (OF-1), and 40% chemical fertilizer reduction with 6000 kg·hm^-2 organic fertilizer (OF-2), We analyzed and compared the soluble nitrogen components, soil nitrogen pool activity (NL), soil nitrogen pool management index (NPMI) and tobacco yield quality of tobacco planting soils under each treatment, and explored the effects of different proportions of organic carbon inputs on the soil NL and NPMI of tobacco planting soils under the condition of continuous chemical fertilizer reduction. The results showed that continuous years of no fertilizer (CK) significantly reduced the tobacco yield, the proportion of medium and top-grade tobacco, and soil soluble nitrogen fraction content and nitrogen pool management index (NPMI). Under continuous fertilizer reduction conditions, different proportions of organic carbon inputs (OF-1 and OF-2) significantly increased flue-cured tobacco yield, soil soluble nitrogen content, soil nitrogen pool activity and nitrogen pool management index. Compared with the CF treatment, soil TDN and DON contents of tobacco plantation in OF-1 and OF-2 treatments increased significantly by 52.11%, 57.36% and 99.25%, 102.64%, respectively; Soil ammonium nitrogen (NH₄⁺-N) and nitrate nitrogen (NO₃^--N) contents increased significantly by 18.08%, 19.22% and 48.08%, 54.61%, respectively; tobacco planting soil nitrogen pool activity increased significantly by 25.88%, 23.03%, and nitrogen pool management index increased significantly by 54.08%, 59.27%, respectively; tobacco yield increased significantly by 18.69%, 19.22%, and the proportion of top-grade and middle-grade tobacco increased significantly by 94.95%, 67.61% and 13.91%, 12.25%, respectively, The effects of OF-1 and OF-2 treatments on soil N pool activity and N pool management index were not significantly different from each other. The results of correlation analysis showed that nitrogen composition, NL and NPMI of tobacco-planting soil were significantly positively correlated with tobacco yield and quality. Random forest analysis showed that soil nitrogen pool management index, soil soluble nitrogen content and soil nitrogen pool activity were important predictors of changes in economic traits of tobacco. In conclusion, under the condition of continuous fertilizer reduction, organic carbon input can increase soil soluble nitrogen content, improve soil NL and NPMI, and promote the improvement of tobacco yield. This can be used as a green ecological fertilization pathway to achieve the efficiency of chemical fertilizer reduction, and can enhance the soil nitrogen supply capacity to achieve high-quality tobacco production.