The study aimed to investigate the effects of sediment types and planting density on the functional traits, growth and community stability of submerged plants, particularly Myriophyllum spicatum. An indoor cultivation experiment was conducted, where different planting densities (1 plant/pot, 10 plants/pot) and sediment types (mud, upper sand + lower mud, sand, upper mud + lower sand) were evaluated for their impact on the species. The findings are as follows: (1) Both sediment types and planting density had significant effects on the morphological characteristics and biomass of M. spicatum; (2) Morphological characteristics: the growth of M. spicatum displayed superior results in all low-density planting conditions compared to high-density; (3) Biomass: planting density had limited impact on biomass allocation patterns within the same sediment type; however, there was a significantly higher in areas with sediment heterogeneity compared to homogeneity. The high morphological plasticity of M. spicatum enables it to adapt to heterogeneous habitats, which likely contribute to its importance as a pioneer species in water restoration projects. These results provide valuable insights for the technical research and development of screening, expansion, colonization and construction, as well as the regulation and management of submerged plant. Moreover, they offer technical support for aquatic ecosystem restoration engineering.