Abstract: Microplastic (the small plastic with the diameter lower than 5 mm) has been widely detected in soil and groundwater worldwide, which draws high attention of researchers and publics as an emerging contaminant. For better predicting and evaluating the environmental risk of microplastic in soil and groundwater environment, mechanism studies focus on microplastic transport are necessary. Nevertheless, transport and retention processes of microplastic in soil and groundwater environment are far from comprehensively known, which should receive more attention. This review summarized the current studies of microplastic source, aggregation, and transport in soil and groundwater environment. Important chemical, physical and biotic factors affecting microplastic transport in soil and groundwater environment were detailly identified and analyzed. The main chemical factors were the hydrochemical condition (e.g. ionic strength, electrolyte type, pH value and dissolved organic matter) and media chemical composition (e.g. Fe/Al oxide ratio and cation release). The main physical factors were the solution flow condition (e.g. flow rate) and media physical composition (e.g. grain size, surface roughness, saturation and heterogeneity). The main biotic factors were the plants (e.g. root development), small soil animals (e.g. movement and ingestion), and microorganisms (e.g. vital activity and basic property). The aggregation of microplastic in water environment was improved with increasing ionic strength, decreasing pH value and dissolved organic matter concentration, and the presence of high valent cations. The transport of microplastic in soil and groundwater environment was enhanced with increasing pH value, media grain size, flow rate and moisture content, however, it was inhibited with increasing ionic strength, surface roughness and electrolyte valence. With the presence of dissolved organic matter, the mobility of microplastic was significantly increased. Microplastic showed a low mobility in porous media containing the high amount of Fe/Al oxide. The transport of microplastic was also decreased if the porous media released cations into aqueous phase. In addition, preferential flow generated in structured heterogeneous media may dominate the transport of microplastic. Root growth and development produced cracks and holes in soils, providing preferential channels for microplastic to vertically migrate. Small soil animals (e.g. earthworms and collembolans) may capture, ingest or carry microplastic and influence its transport behavior subsequently. Microorganisms (e.g. bacteria and algae) living on the surface of porous media may capture or adsorb moving microplastic, which then may increase the retention and decrease the transport of microplastic in soil and groundwater environment. The related impact mechanism of the factors mentioned above were systematically discussed and visually illustrated by schematic diagrams. At the end of this review, current knowledge gaps and prospective topics needed to be promoted were highlighted for further developing and investigating the fate and transport of microplastic in soil and groundwater environment. Given current researches were almost limited to laboratory scale and polystyrene microsphere, field researches (e.g. lysimeter experiments), diversified type, the basic property and transform researches should be emphasized on in future microplastic transport studies. This review contributes to expanding our knowledge of fate and transport of microplastics in soil and groundwater environment.