Standard　mica　was　used　to　correct　the　X-ray　powder　diffraction　instrument　error　and　mathematic　methods　were　employed　to　find　the　correction　equation.　By　analyzing　mullite　sample　and　comparing　the　corrected　and　uncorrected　analysis　results　we　found　the　former　is　obviously　more　reasonable.　So　the　conclusion　is　that　the　X-ray　powder　diffraction　instrument　error　greatly　affects　the　crystalline　structure　analysis,　and　the　above　method　is　convenient　and　effective　for　the　correction　of　instrument　error.