The present invention relates a use of EGFR/HER2 receptor tyrosine kinase inhibitor in the preparation of a medicament for the treatment of HER2 mutation cancer. Specifically, the present invention relates a use of compound of formula A or its medicinal salt in the preparation of a medicament for the treatment of HER2 mutation cancer.本發明涉及一種EGFR/HER2受體酪胺酸激酶抑制劑在製備治療HER2突變癌症藥物中的用途。具體而言涉及式A所示化合物或其可藥用鹽在製備治療HER2突變的癌症的藥物中的用途。