Waste　aluminum　sludge,　talc　powder　and　clay　were　used　to　synthesize　cordierite　in　this　research.　The　impurities,　such　as　Fe2O3,　CaO,　K2O　and　Na2O,　in　the　raw　materials　have　some　influence　on　the　structures　and　properties　of　the　materials.　In　this　paper,　we　mainly　discuss　the　impact　of　impurity　Na2O　on　the　structure　of　cordierite,　based　on　which　the　permitted　amount　of　Na2O　was　determined.　The　results　show　that　Na2O　with　the　amount　less　than　0.6%　has　little　influence　on　the　cordierite　formation;　while　when　its　amount　increasing　from　0.6%　to　0.7%,　the　content　of　cordierite　decreases　from　86%　to　84%　and　the　permitted　amount　for　Na2O　in　the　raw　materials　is　less　than　6%　with　the　best　amount　less　than　0.3%.　X＇pert　plus　software　analysis　results　show　the　impurity　Na2O　has　no　influence　on　the　cordierite　space　group　and　only　the　lattice　parameters　vary　slightly;　but　it　has　much　influence　on　the　structure　of　Mg-Al　spinel　and　the　lattice　parameters　are　much　changed.