OBJECTIVE To evaluate the economics of serplulimab combined with chemotherapy regimens for the first-line treatment of extensive-stage small cell lung cancer （ES-SCLC） from the perspective of health system in China. METHODS A partitioned survival model was constructed based on the ASTRUM-005 clinical trial and related literature data， with a model simulation time frame of 10 years and a 3-week cycle， and both cost and utility values were discounted using a 5% discount rate. The quality-adjusted life year （QALY） was used as a model output indicator and the incremental cost-effectiveness ratio （ICER） was calculated to evaluate the economics of serplulimab combined with chemotherapy regimens （serplulimab group） versus chemotherapy alone regimens （chemotherapy alone group） for the first-line treatment of ES-SCLC. One-way sensitivity analysis and probabilistic sensitivity analysis were used to verify the robustness of the results of the base-case analysis and to conduct a scenario analysis for the serplulimab patient assistance program. RESULTS The results of the base-case analysis showed that compared with chemotherapy alone group， ICER of serplulimab group was 758 690.27 yuan/QALY， which was higher than 3 times China’s per capita gross domestic product （GDP） in 2022 as the willingness-to-pay （WTP） threshold. The results of the scenario analysis showed that compared with chemotherapy alone group， the ICER of serplulimab group was 172 275.74 yuan/QALY， which was below above WTP threshold. The one-way sensitivity analysis showed that the progress-free survival utility value， serplulimab price and so on had a significant impact on the model results. The results of the probabilistic sensitivity analysis showed that the probability of the serplulimab group being economic was 0 when the serplulimab patient assistance program was not considered， but 100% when the patient assistance program was considered. CONCLUSIONS At a WTP threshold of 3 times China’s per capita GDP in 2022， the serplulimab group is no cost-effectiveness compared to the chemotherapy alone group； however， this result is reversed when the patient assistance program is taken into account.