Waste　aluminum　slag　and　silica　powder　from　ferroalloy　plant　as　the　main　raw　materials　and　BaF2　or　TiO2　as　mineralizers　respectively,　were　used　to　synthesize　mullite.　The　reaction　mechanism　of　mineralizers　(BaF2　and　TiO2)　and　the　influence　of　the　contents　of　mineralizers　on　the　microstructure　of　mullite　was　studied.　The　crystal　phase　and　microstructure　of　sample　synthesized　were　characterized　by　X-ray　diffraction　and　scanning　electron　microscopy.　Semi-quantitative　software　(Rietveld　Quantification)　was　applied　to　calculate　the　content　of　each　crystalline　phase.　The　results　show　that　mullite　exists　as　a　solid　solution　form.　When　2.5%　(in　mass,　the　same　below)　BaF2　was　added,　the　content　of　mullite　in　the　synthesized　sample　reached　the　highest　value　(95%).　The　micro-structure　of　the　sample　are　mainly　in　granular　and　column　shapes.　Furthermore,　when　1.0%　TiO2　is　added,　the　content　of　mullite　reaches　to　96%,　and　the　mullite　crystal　grains　are　in　small　needlelike　shapes.