Fibrous　porous　media　plays　an　important　role　in　aerosol　or　small　particle　filtration.　The　filtration　of　fibrous　porous　media　is　a　composite　process,　of　which　the　filtration　performance　is　affected　by　many　parameters　and　is　quite　difficult　to　be　predicted　precisely.　In　this　paper　the　parameters　affecting　the　filtration　performance　are　re-examined.　Especially,　the　influences　of　fiber　sizes　and　the　porosity　of　the　porous　media　to　the　filtration　efficiency　are　analyzed　further.