Analyzes of leachate from several landfill sites in Fukushima Prefecture have shown that most of the sites have radioactive cesium concentrations as low as a few becquerel, but in some disposal sites it showed values exceeding 10 Bq/kg. In order to clarify the behavior of seepage water flowing inside the waste disposal site under the conditions that do not contain radioactive materials, therefore, numerical simulations were conducted using a system that simply simulates a structure of landfill materials accumulated in layers in the vertical direction. The effect of porosity in landfills on seepage water behavior was investigated. When the porosity is large, there are large spaces in the landfill, and it takes time for seepage water to fill the spaces. As a result, it was found that the time required for seepage water to move to the bottom of the waste disposal site was longer than when the porosity was small. The prospect of qualitatively evaluating the tendency of movement behavior of seepage water by simulation was obtained.