Introduction Flumatinib is a novel second-generation BCR-ABL1 targeted kinase inhibitors (TKI) with better efficacy and safety than first generation TKIs in first-line treatment of chronic myeloid leukemia in chronic phase (CML-CP). In the previous phase III study, newly diagnosed CML-CP patients receiving flumatinib achieved higher treatment responses and safety than imatinib. When it comes to the patients not achieving the optimal response to TKIs, flumatinib is potentially a better option, nonetheless the robust evidence is unavailable. This study reports the effectiveness and safety of switching to flumatinib in patients who have not achieved the optimal molecular response to imatinib or/and dasatinib.