Infiltration experiment on soil columns of homogeneous loam and loam with a sand interlayer under ponding conditions were conducted in laboratory. The influence of sand interlayer on infiltration rate, wetting front advancement and the variation of water content along the soil profile was monitored and analyzed. After the wetting front reached the upper interface of the sand interlayer, the infiltration process of the loam with sand interlayer was distinctly different from that of the homogeneous soil, and the infiltration rate varied greatly. Finally a steady infiltration stage reached, and the steady infiltration rate was smaller than that of the homogenous soil. When the wetting front passed the sand interlayer, water content inside this coarse interlayer was less than the saturated water content. According to the observation and analysis, S-Green-Ampt model was established to describe the infiltration process with coarser interlayer. This model can more accurately reflect the mechanism of infiltration into layered soils and better describe the infiltration process of soil with sand interlayer.