A pot experiment was carried out on effects of different humic acid and nitrogen levels and their interaction on tobacco planting soil aggregate composition, nutrient and enzyme activity with the flue-cured tobacco variety of zhongyan100. The results showed that the soil aggregate mean weight diameters of the treatment with T3(300 mg/kg humic acid + 40 mg/kg nitrogen) were the highest in both dry and wet sieving method, and compared with those of the other treatments, they were increased by 15.3 percent to 23.2 percent and 6.5 percent to 20 percent, respectively. Variance analyses showed that the interactions of humic acid and nitrogen were not significant on soil pH and organic matter, but extremely significant on soil available nitrogen, available phosphorus and available potassium contents (P<0.01), and different on soil urease and invertase activities in each growing period. The results indicated that humic acid, nitrogen and their interactions have significant effects on improving soil aggregate stability, soil nutrient contents and soil enzyme activities.