Abstract: The nutrient solution is standing in existing floating system, it restrains the growth of root system and results in uneven growth of seedlings, therefore the floating system was improved, an automatic nutrient solution circulating system and a tobacco seedling cultivating method relevant to that system were developed. The results showed that in the improved system, the concentration of dissolved oxygen in circulated nutrient solution increased to 2.24 mg/L, the length and biomass of roots raised obviously, the growth rate of tobacco seedlings accelerated and the seedling stage reduced by 9 days comparing with that of control. The contents of chlorophyll, soluble protein and free amino acids in seedlings increased and the physiological quality of seedlings improved. It was concluded that nutrient solution circulation was beneficial to breeding strong tobacco seedlings.