Hydrilla verticillata is a common submerged plant in shallow lakes in China, and is often used as a pioneer species in lake ecological restoration projects. However, the Hydrilla verticillata tends to overgrowth, forming a canopy which affects other functions of lakes. Lanthanum-modified bentonite (Phoslock^®) can effectively reduce the bioavailable phosphorus content in sediments. In recent years, it has been used to control phosphorus release from lake sediments. Its impact on the growth and morphology of Hydrilla verticillata remains to be clarified. In this study, two treatments with and without Phoslock^® in the sediments were set up to investigate the effects of Phoslock^® on the growth and morphological characteristics of Hydrilla verticillata under two different water nutrient concentrations. The results show that:1) After adding Phoslock^® to the sediments, the bioavailable phosphorus concentration, such as Fe/Mn combined phosphorus (BD-P), organic phosphorus (Org-P), Aluminum-bound phosphorus (Al-P), is significantly reduced, while the non-bioavailable phosphorus concentration, such as Calcium-bound phosphorus (Ca-P), is significantly increased. 2) The addition of Phoslock^® in the sediments significantly reduced the biomass and growth rate of the Hydrilla verticillata. The plant height and aboveground biomass of Phoslock^® group were significantly lower than those without Phoslock^®; on the contrary, the addition of Phoslock^® significantly increased the root length of the plant and the underground biomass, and increased the plant's root-shoot ratio. 3) The effect of Phoslock^® on the growth of Hydrilla verticillata is related to the concentration of nutrients in the water, and the effect of Phoslock^® on plant growth and morphological characteristics is more significant in low-nutrient water. Overall, this study shows that the addition of Phoslock^® can effectively reduce the concentration of bioavailable phosphorus in sediments and inhibit the growth of Hydrilla verticillata, and this effect is more significant when the concentration of nutrients in the water is reduced.