[Objective] The effects of microplastic type and size on the infiltration process of carbonatite laterite soils was investigated in order to provide new data revealing the hydrological processes of microplastic-contaminated agricultural soils. [Methods] The effects of polyethylene (PE), polypropylene (PP), and polystyrene (PS) microplastics with different particle sizes (550, 150, and 50 μm) on the infiltration rate, cumulative infiltration, and the depth of the wetting front of the lateritic soil were investigated by an indoor simulation of infiltration into a flattened soil column using a fixed-head vertical infiltration method. The effects of the cumulative infiltration, Philip, Horton, and Kostiakov models on the infiltration rate of the lateritic soil, cumulative infiltration, and the depth of the wetting front were also evaluated. The five hydraulic parameters (θ_r, θ_s, α, n, K_s) were inverted under different microplastic treatments using the Hydrus-1D model. [Results] ① The infiltration rate and cumulative infiltration of PS microplastics increased with decreasing particle size, while the cumulative infiltration and infiltration rate of PE and PP microplastics increased and then decreased with increasing particle size, and the differences in cumulative infiltration between different particle sizes were significant (p＜0.05); PS microplastics facilitated and then inhibited water transport, while both PP and PE played the role of facilitating water transport. ② All models were applicable to the infiltration simulation of microplastic-containing laterite soils, with Horton’s model and the cumulative infiltration model performing the best (R², CE > 0.98). ③ The effect of microplastic treatment on soil hydraulic parameters (θ_r, θ_s, α, n, K_s) was insignificant, but the PS microplastic saturated hydraulic conductivity showed an increase with decreasing particle size. [Conclusion] The effects of PS, PP, and PE microplastics on soil infiltration processes were significantly different, and the Horton, cumulative infiltration, and Hydrus-1D models showed high applicability.