Although pervasive microplastics (MPs) pollution in terrestrial ecosystems invites increasing global concern, impact of MPs on soil microbial community assembly and ecosystem multifunctionality received relatively little attention. Here, we manipulated a mesocosm experiment to investigate how polyethylene MPs (PE MPs; 0, 1%, and 5%, w/w) influence ecosystem functions including plant production, soil quality, microbial community diversity and assembly, enzyme activities in carbon (C), nitrogen (N) and phosphorus (P) cycling, and multifunctionality in the maize-soil continuum. Results showed that PE MPs exerted negligible effect on plant biomass (dry weight). The treatment of 5% PE MPs caused declines in the availability of soil water, C and P, whereas enhanced soil pH and C storage. The activity of C-cycling enzymes (α/β-1, 4-glucosidase and β-D-cellobiohydrolase) was promoted by 1% PE MPs, while that of β-1, 4-glucosidase was inhibited by 5% PE MPs. The 5% PE MPs reduced the activity of N-cycling enzymes (protease and urease), whereas increased that of the P-cycling enzyme (alkaline phosphatase). The 5% PE MPs shifted soil microbial community composition, and increased the number of specialist species, microbial community stability and networks resistance. Moreover, PE MPs altered microbial community assembly, with 5% treatment decreasing dispersal limitation proportion (from 13.66% to 9.96%). Overall, ecosystem multifunctionality was improved by 1% concentration, while reduced by 5% concentration of PE MPs. The activity of α/β-1, 4-glucosidase, urease and protease, and ammonium-N content were the most important predictors of ecosystem multifunctionality. These results underscore that PE MPs can alter soil microbial community assembly and ecosystem multifunctionality, and thus development and implementation of practicable solutions to control soil MPs pollution become increasingly imperative in sustainable agricultural production.