Coal-tar　pitch　is　widely　used　to　prepare　composite　materials　by　the　several　cycles　of　impregnation　and　carbonization.　Impregnation　becomes　the　control　step　for　cost　when　the　high-density　carbon　preform　is　densified.　Thus,　effects　of　additives　on　the　permeability　of　the　pitch　are　investigated　by　experiments　and　their　mechanisms　are　discussed　according　to　theoretical　analysis　of　fluid　kinetics.　Direactive　glyceride　as　well　as　aluminum　sulfate　and　polyethylene　oxides　evidently　increase　permeability　by　changing　the　physical　structure　of　pitch.　However,　divinylbenzene　has　chemical　modification　to　the　pitch　in　the　presence　of　p-toluene　sulfonic　acid,　which　leads　to　a　marked　decrease　in　permeability.　In　this　regard,　the　former　two　types　of　additives　are　more　suitable　than　the　latter　one　to　modify　the　coal-tar　pitch　as　a　precursor　to　densify　the　carbon　preform　with　high　density.　In　addition,　the　permeability　drastically　depends　on　the　concentrations　of　additives.　©　2005　Elsevier　B.V.　All　rights　reserved.