The long-term service performance of road structures is closely related to the subgrade humidification state. To study the moisture-controlling effect of fine-grained soil subgrade under rainfall infiltration， the typical silty clay subgrade fills in the middle and lower reaches of the Yellow River basin in China were selected in this paper. The hydrodynamic properties of silty clay and wicking geotextile were obtained based on the test of the pressure plate instrument， and the physical model of wicking geotextile-reinforced silty clay was constructed to investigate the migration of the water in the silty clay fill under different rainfall intensities. The development of soil moisture content and matric suction was obtained with or without the wicking geotextile. Results indicate that the wicking geotextile has a higher lateral permeability coefficient （2.2 cm/s）， lower water-holding capacity， and air entry value （2.8 kPa）， which can realize the lateral drainage of water under low matric suction. The migration of water inside the soil under rainfall infiltration is subjected to the combined effect of gravity potential and matric potential， and the existence of the wicking geotextile can increase the matric suction of the soil layer by 5.1~34 kPa. The soil above the geotextile is driven by gravity potential and matric potential together， and the moisture migrates from up to down. However， for the soil below the geotextile， the matric potential needs to overcome the effect of gravity potential， and drive the moisture to migrate from down to up. The moisture content of the wicking geotextile-reinforced soil is reduced from 13.8% （light rain）~17.2% （heavy rain） in the control group to 12.6% （light rain） ~ 14.0% （heavy rain）， which can be effectively controlled within ωopt+2%， which is of great practical value for guaranteeing the long-term service life of the roadbed pavement.