Abstract: In order to understand the plasticity of submerged macrophytes to environmental variations, an experiment on the g～owth response of Hydrilla verticillata to two sediment types (sand, clay+sand) and three densities was made. The results showed that compared with to sand sediment, (clay+sand) sediment greatly increased the plant height and stem diameter and decreased the root biomass allocation (P<0. 05). Lower density significantly increased the stem biomass allocation while decreased the leaf biomass ratio (P<0.05).’ For sand, plants at high density grew better, e. g., a great increase in relative growth rate and biomass (P<0.05). However, for clay+sand, density had an opposite influencing pattern, i. e., plants at high density had a slower growth (P<0.05). At high density, sand increased plant growth (P<0.05). At lower density, plants at (clay+sand) sediment grew faster (P