Abstract: Disclosed are applications of humic acid (HA) in improving phytoremediation efficiency of heavy metals in waterbody, relating to the technical field of environmental ecological engineering. The phytoremediation of heavy metals is achieved by reducing heavy metals content in the waterbody by planting Vallisneria natans. HA is added to slow down the degreening of Vallisneria natans leaves under heavy metal toxicity, and to increase the accumulation of leaves and roots of Vallisneria natans to heavy metals, together with reducing the leaching capacity of heavy metals in waterbody; HA enhances the activity of enzymes related to reactive oxygen metabolism in plants by stimulating the synthesis of proteins and enzymes in various organs of plants, as well as reducing the concentration of malondialdehyde in plants, regulating the reactive oxygen content in plants, reducing the peroxidation of membrane lipids, and enhancing the resistance of plants to heavy metals.