Abstract: In order to find a solution to the problems of slow restoring and poor drought tolerance of flue-cured tobacco seedlings in float system, the experiment of seedling hardening at two different water levels:low water level (the bottom of seedling tray touching on the water surface) and extra-low water level (the bottom of seedling tray over the water surface by 5cm) was conducted by using conventional float system practice as the control. The results showed that:the biological characteristics of seedlings in low water level treatment were better than that in extra-low water level treatment, both treatments were better than the control. The restoring rate, root system vigor, nitrate reductase activity, photosynthetic rate and chlorophyll content of tobacco seedling were better in extra-low water level treatment and good in low water level treatment.