To investigate the micro-mesoscopic structure and mechanism of plant-stabilized microplastic-contaminated tailings soil under different freeze-thaw cycles, the Waitoushan tailings pond of Benxi Iron and Steel Group was selected as the research background. Scanning electron microscopy and X-ray diffraction tests were conducted. The effects of microplastic content, root exudate diversity, and freeze-thaw cycles on the microstructure of tailings soil were investigated.The results show that the pore structure of tailings soil is changed by microplastic addition. The number of pores is increased. The pore size distribution becomes more discrete. The pore channels become more tortuous. Structural loosening is intensified by a high microplastic content. The microstructure of tailings soil is reconstructed by root exudates. In particular, particle aggregation is promoted by high-diversity root exudates. The proportion of large pores is reduced. The structural compactness is improved. Freeze-thaw cycles have a staged damage effect on tailings soil. Pure tailings soil shows an evolution pattern of “early compaction and later crack expansion”. Crack penetration is inhibited to some extent by microplastics. Pore expansion and structural reconstruction are enhanced by root exudates. Under the coupled effects of the three factors, the pore system of tailings soil shows multiphase coupling and multiscale evolution characteristics. The results provide a reference for the remediation of microplastic-contaminated tailings in seasonally frozen regions.