A water-level adjusting method used in a hydroponic tank is provided. An apparatus thereof and a plant cultivating apparatus are also provided. The hydroponic tank is used to grow a plant. The water-level adjusting method includes: sensing a minimum horizontal level of the plant along the growth direction of the root of the plant by a sensor； and adjusting the water level of the hydroponic tank according to the minimum horizontal level. Therefore, the costs of labor and time are saved by using the water-level adjusting method provided herein instead of using the traditional way which adjusts the water level of the hydroponic tank manually.一種水耕槽的水位調節方法，其中水耕槽適於栽培植株。水位調節方法包括下列步驟。藉由感測器沿植株的根系生長方向感測植株的最低水平高度。依據最低水平高度調節水耕槽的水位高度。基此，可取代傳統使用人工調節水耕槽的水位高度的方式，降低使用水耕槽栽培植株時付出的人力成本與時間成本。此外，一種水耕槽的水位調節裝置與一種植物栽培裝置亦被提出。
