The study of DESTINY-Lung01 and DESTINY-Lung02 demonstrated the favorable efficacy and optimal dosage of trastuzumab deruxtecan (T-DXd) in managing the human epidermal growth factor receptor 2 (HER2)-mutant non-small cell lung cancer (NSCLC) patients who had received previous treatment. The study sought to assess the cost-effectiveness of T-DXd in both the United States (US) and Chinese healthcare systems. Markov models were developed to evaluate the overall cost, incremental cost-effectiveness ratio (ICER), quality-adjusted life years (QALYs), and life years (LYs) of treatment with T-DXd compared with docetaxel, nivolumab, and pyrotinib for patients in the US and China. The level of willingness-to-pay (WTP) in the US and China is 150,000/QALYs and 32,517/QALYs, respectively. Sensitivity analyses were carried out to ensure the precision of the model. T-DXd yielded additional QALYs of 0.63 and 0.06 with an ICER of 38997.84 and 437258.33 per QALY, respectively, in the US compared to the docetaxel and nivolumab regimens. And T-DXd yielded additional QALYs of 0.63, 0.06, and 0.13 with an ICER of 37959.45, 23805.93, and 15447.12 per QALY, respectively, in China compared to the docetaxel, nivolumab, and pyrotinib regimens. Sensitivity analysis showed that the cost of drugs is the most influential factor. T-DXd provides substantial therapeutic benefit for NSCLC patients with HER2 mutations who have had previous treatment but is not deemed cost-effective in either the US or China when compared to docetaxel, nivolumab, and pyrotinib. Price reduction is perhaps the main way to make T-DXd cost-effective.