The present disclosure provides the use of acetyltanshinone IIA in the preparation of medicament for treating lung cancer and medicament for treating lung cancer, which falls within the technical field of medicine. This protocol proposes the use of acetyltanshinone IIA in treating lung cancer, especially non-small cell lung cancer (NSCLC), which can antagonize primary and acquired drug resistance of NSCLC cells to epidermal growth factor receptor, tyrosine kinase inhibitor (EGFR TKIs), by using small molecule compound acetyltanshinone IIA. The present disclosure further identifies the molecular target of ATA and elucidates its mechanism of inhibiting the growth of drug-resistant NSCLC cells and tumors. The medicament containing acetyltanshinone IIA is expected to become a multi-target anticancer agent for treating TKI drug-resistant NSCLC.