A hydroponic system consists of a hydroponic tank, a carrier or carriers for carrying or growing plants, a float or floats, and a supplementary lifting unit. The supplementary lifting unit includes a take-up mechanism having a small reel and one or multiple large reels configured subject to the circumference ratio of 1:≧1 so that increasing the fluid level in the hydroponic tank to lift or lower the float one unit-height causes the carriers and the plants thereof to be lowered or lifted one unit-height plus the height corresponding to the circumference ratio between the large reel and the small reel for enabling the roots, stems and leaves of the growing plants to be dipped in the nutrient solution in the hydroponic tank or exposed to the outside air.
