Abstract: Regular water requirement of flue-cured tobacco at fast growing stage was studied. The results showed that the optimum relative water content was in a range of 75% -85% of the mass of soil, in which water -utilization efficiency of tobacco plant was the highest, CO₂ and moisture exchange between stomata of tobacco leaves and ambient air was the easiest, and the growth of root, stalk, and leaf of tobacco plant was the fastest.