Microplastics are contaminants of emerging concern. In particular, research on the ecological effects of microplastics on microorganisms has attracted widespread attention. In this study, the role of characteristics of microplastics and environmental factors on microorganisms in sediments along the Daihai Lakeshore were investigated. Microscopic identification of microplastics revealed that the most common characteristics of microplastics were fiber, black color and particle size <0.5 mm. The results of Pearson correlation analysis verified that the characteristics of microplastics with particle size <0.5 mm and the main physicochemical characteristics of the sediments (pH, salinity) were positively correlated with the abundance of dominant microorganisms (P < 0.05). In addition, Kyoto Encyclopedia of Genes and Genomes (KEGG) functional pathway analysis that the proportion of functional metabolic pathways related to DNA replication, recombination and reparation was higher in the sampling sites with higher microplastics abundance. This study will provide valuable information for assessing the microbial ecological effects of microplastics contamination in sediments.