Soil’s hydraulic properties are an essential characteristic that influences the hydrologic cycle by influencing infiltration and runoff and the transport of soil water and salt in the process of vegetation rehabilitation in coastal saline soils. To date, few studies have specifically addressed the soil’s hydraulic properties and root–soil interactions of coastal saline soil under revegetation. This study aimed to identify the unique hydraulic characteristics of soil, the pore size distribution parameter, Gardner α, and the different contributions of soil’s physical properties and vegetation’s root morphological characteristics with regard to soil infiltration. For this purpose, disc infiltration experiments at different pressure heads were performed on three vegetation types, Salix matsudana (SM), Hibiscus syriacus (HC), and Sabina vulgaris (SV), after two years of vegetation rehabilitation. The results demonstrated that the initial and steady infiltration rate, Gardner α, and soil porosity fraction exhibit significant differences among the three plant species. A correlation analysis indicated that the soil water content, surface area, density, and dry weight of roots had inverse relationships with soil infiltration at heads of pressure of 0 cm and 9 cm. The regulation of soil infiltration was influenced by the root dry weight and root average diameter, which played crucial roles in determining the roots’ morphological properties and the formation of pathways and soil pores.