An external cultivation liquid siphon includes a liquid delivery equipment located in a cultivation liquid storage tank to continuously pump cultivation liquid to a plant cultivation pot and an external siphon equipment to bridge the cultivation liquid storage tank and the plant cultivation pot. The external siphon equipment has a tubular facility with variations in tubular diameters to generate siphonage action to fill the tubular facility with flowing liquid. Thus the cultivation liquid pumped by the liquid delivery equipment to the plant cultivation pot can circulate reciprocally between an upper liquid level and a lower liquid level to cultivate plants.
