Abstract: To make certain of the promoted action of humic acid on the growth of flue-cured tobacco, the influence of 0, 20, 40, 60, 80, 100mg/kg humic acid on root biomass, stem-leaf biomass and root system vigour of flue-cured tobacco were studied in this paper by nutrient solution?water planting test. The result indicated that 10d, 20d, 30d after incubation, the root fresh weight, root dry weight, root system vigour, stem-leaf fresh weight and stem-leaf dry weight of water planting tobacco increased with the humic acid concentration raising within 20mg/kg~60 mg/kg. The 60mg/kg concentration humic acid, which was the concentration of the highest volume for each aforementioned index, can promote the growth of tobacco plant. At the condition of above 60mg/kg concentration humic acid, the root fresh weight, root dry weight, root system vigour, stem-leaf fresh weight and stem-leaf dry weight of water planting tobacco decreased with the humic acid concentration rise, then the growth of tobacco was inhibited.