Abstract: The silty soil is modified by polymer materials. Based on the relationship among unconfined compressive strength, dry density and water content, the optimum water content of the silty soil modified by the polymer materials is determined. In order to investigate the behaviors of the silty soil modified by the polymer materials with the optimum water content, the permeability tests, capillary water rising tests, anti-scour tests under varing precipitation time as well as strength characteristics test under wetting-drying circles are conducted. The test results are as follows: (1) the permeability coefficient greatly decreases due to being mixed with polymer materials; (2) the capillary water function is improved, and capillary water effect of lifting height greatly decreases; (3) with the increase of the precipitation time, the mass loss of soil samples increases; (4) anti-scour characteristics are good; and (5) the strength degradation is weak and the failure strain and the maximum stress both change very little with the increase of the wetting-drying cycles. The conclusion is that the silty soil modified by the polymer materials is of better water stability and is suitable to be used as subgrade fill for expressways in silt areas.