The　void　parameters　such　as　void　radius　and　void　space　are　achieved　by　image　analysis　of　porous　asphalt　mixture　sample　slice　through　cosmos　image　analyzing　software,　so　as　to　set　up　the　grid　sizing　of　the　permeability　model　of　the　porous　asphalt　mixture　and　the　input　of　original　value.　The　method　of　Monte　Carlo　is　used　to　set　up　the　permeability　model.　The　mathematics　model　abstracted　is　based　on　the　Hagen-Poiseuille　theory　and　the　flab　iterative　method.　The　result　shows　that　the　numerical　simulation　permeability　outcome　is　consistent　with　the　indoor　permeability　test　outcome.　The　model　can　simulate　any　maximum　congregate　diameter　at　different　water　surface　levels　and　the　permeability　coefficient　of　any　open-graded　porous　asphalt　mixture.　The　model　offers　an　effective　method　for　designing　of　the　porous　asphalt　mixture.