The effects of polystyrene microplastics (PS-MPs) with mass fractions of 0.0% (CK), 0.5%, 1.0%, and 2.5% (based on dry mass of sediment) on the growth traits, leaf chlorophyll contents, and antioxidant system of Myriophyllum verticillatum Linn., as well as rhizosphere and sediment bacterial communities were analyzed by a greenhouse control experiment. The results show that PS-MPs significantly inhibit (p<0.05) plant height, root length, dry mass per plant, and chlorophyll content of M. verticillatum in general, and the inhibitory effect intensifies with the increase of mass fractions. PS-MPs have the effect of low mass fraction promotion and high mass fraction inhibition on the antioxidant enzyme activities of M. verticillatum leaves: compared with the CK group, the activities of superoxide dismutase, peroxidase, and catalase in the 0.5% (mass fraction) PS-MPs treatment group increase by 7.52%, 11.43%, and 12.36%, respectively, while those in the 2.5% (mass fraction) PS-MPs treatment group decrease by 16.30%, 16.14%, and 35.44%, respectively. Malondialdehyde content increases with the increase of mass fractions of PS-MPs, indicating aggravated membrane lipid peroxidation damage. The addition of PS-MPs alters the rhizosphere bacterial community structure of M. verticillatum, but exerts minor effects on sediment bacterial community structure. Compared with the CK group, the proportion of Actinomycetota in the rhizosphere bacterial community of M. verticillatum decreases in PS-MPs treatment groups, whereas the proportion of Pseudomonadota increases and becomes the most dominant phylum. In conclusion, PS-MPs significantly inhibit the growth of M. verticillatum by changing its physiological characteristics; meanwhile, the effects of PS-MPs on bacterial community structures of M. verticillatum rhizosphere may indirectly interfere with the physiological metabolism of M. verticillatum.