Abstract: A field experiment was carried out to study the effect of nitrogen management on soil Nmin, soil carbon and the enzyme activities in tobacco rhizosphere under the optimization of C/N with organic fertilizers. The results showed that:(1) In the lower nitrogen treatments N1 and N2, NH₄⁺-N contents in the rhizosphere soil decreased during the growth season while in the higher nitrogen N3 treatment, NH₄⁺-N content increased at the rosette to vigorous growth stage, then decreased,.and nitrate nitrogen decreased for all treatments; (2) The microbial carbon and nitrogen increased with the nitrogen level and the growth process. (3) The soil urease and invertase activities increased with the nitrogen level, the soil urease activities were slightly reduced in the lower N1 and N2 treatments at the mature stage, whereas that of the higher N3 treatment increased during the whole growth period; The soil invertase activities were higher at the rosette stage in the S1 and S2 treatments, while it was higher after the rosette stage in S3 treatment. In the higher nitrogen level treatment (N3), soil nitrogen was continuously excessively supplied, and nitrogen was not reduced to the "nitrogen deficit" level during the mature period, which led to reduced tobacco quality; while at the N2 level, the soil urease activities of the S3 treatment increased first then decreased, which was more consistent with the nitrogen demand of the plants.