The　polycrystalline　structure　of　mullite-cordierite　polyphase　material　and　its　contents　were　determined　by　XRD　and　SEM,　respectively.　The　influence　of　different　contents　of　silica　fume　on　the　structure　and　properties　of　the　polyphase　material　was　discussed.　It　is　demonstrated　that　four　crystalline　phases,　alpha-Cordierite,　beta-cordierite,　mu-cordierite　and　mullite,　exist　in　the　polyphase　material.　The　content　of　cordierite　increases　while　that　of　the　mullite　decreases　with　the　increase　of　silica　fume.　The　optimum　formulation　is　as　follows:　cordierite　66.3%,　mullite　33.7%　(one　time)　and　47.35%　(ten　times),　and　bulk　density　of　2.69　g/cm(3).