The invention discloses a tobacco floating seedling growing method. The method comprises the steps of pouring a medium into a stray, sowing in a floating tray, managing fertilizer, managing water, managing plant diseases and insect pests, managing leaf cutting, and managing temperature. The fertilizer management comprises the steps that before the floating tray is placed into water, the electricalconductivity of tank water in a seedling growing tank is 0.1-0.35 mS/cm; 7-10 days after the floating tray is placed into water, the first fertilization is carried out, the nitrogen concentration is100-160 N ppm, after the fertilizer evenly disperses in the seedling growing tank, the electrical conductivity of the tank water in the seedling growing tank is measured, and the electrical conductivity of the tank water is controlled at 1.25-2.18 mS/cm; 28-35 days after the floating tray is placed into water, the first additional fertilization is carried out, the nitrogen concentration is 100-130N ppm, after the fertilizer evenly disperses in the seedling growing tank, the electrical conductivity of the tank water in the seedling growing tank is measured, and the electrical conductivity of the tank water is controlled at 1.25-1.82 mS/cm; 38-45 days after the floating tray is placed into water, the second additional fertilizer is applied, the nitrogen concentration is 50-80 N ppm, after the fertilizer evenly disperses in the seedling growing tank, the electrical conductivity of the tank water in the seedling growing tank is measured, and the electrical conductivity of the tank water is controlled at 0.67-1.26 mS/cm.