Objective:To investigate the efficacy and safety of immune checkpoint inhibitors (ICI), programmed death receptor 1 (PD-1) inhibitors and programmed death receptor-ligand 1 (PD-L1) inhibitors in the treatment of extensive-stage small cell lung cancer (ES-SCLC).Methods:The databases of CNKI, Wanfang, VIP, China Biology Medicine disc, PubMed, Embase, and Cochrane Clinical Controlled Trial Center Registry (CENTRAL) were retrieved, and the randomized controlled trial literature on the treatment of ES-SCLC with immune checkpoint inhibitors published from the establishment of the database until October 4, 2023 were reviewed. After screening literature and extracting data according to inclusion and exclusion criteria, the risk of bias in the study was evaluated using Review Manager 5.4 software. The disease remission, prognosis and adverse events (AE) of patients treated with ICI combined with chemotherapy (experimental group) and placebo± chemotherapy (control group) in the whole group and liver metastases and brain metastases subgroups were compared.Results:A total of 11 randomized controlled trials were included, with 2 243 cases in the experimental group and 2 059 cases in the control group. The included research data were complete and showed no selective bias. Compared with the control group, the objective response rate (ORR) of patients in the experimental group was higher [control group vs. experimental group, 64% (864/1 358) vs. 70% (1 088/1 532), RR = 1.08 (95% CI: 1.03-1.14), P = 0.003], and the difference was statistically significant; progression free survival (PFS) [experimental group vs. control group, the median PFS time, 5.14 months (95% CI: 4.88-5.40 months) vs. 4.76 months (95% CI: 4.70-4.82 months), HR = 0.72 (95% CI: 0.67-0.78), P < 0.001] and overall survival (OS) [experimental group vs. control group, the median OS time, 12.89 months (95% CI: 12.18-13.60 months) vs. 10.41 months (95% CI: 10.03-10.79 months), HR = 0.72 (95% CI: 0.67-0.78), P < 0.001] were all improved, and the differences were statistically significant. The OS of patients with baseline liver metastasis in the experimental group was better than that in the control group (experimental group vs. control group, HR = 0.82 (95% CI: 0.71-0.95), P = 0.009], and the difference was statistically significant, while the difference in OS of patients with baseline brain metastases was not statistically significant between the experimental group and the control group [experimental group vs. control group, HR = 0.84 (95% CI: 0.66-1.08), P = 0.170]. The incidence of AE [experimental group vs. control group, 31% (597/1 952) (95% CI: 24%-37%) vs. 14% (255/1 762) (95% CI: 9%-22%), RR = 2.25 (95% CI: 1.67-3.02), P < 0.001] and the incidence of drug discontinuation or dose change caused by AE [experimental group vs. control group, 21% (379/1 774) (95% CI: 12%-41%) vs. 19% (307/1 588) (95% CI: 6%-25%), RR = 1.20 (95% CI: 1.07-1.33), P = 0.001] in the experimental group were higher than those in the control group, and the differences were statistically significant. However, the incidence of severe (≥grade 3) AE in both the experimental group and the control group was 34% (620/1 814, 557/1 632) (both 95% CI: 32%-36%), and the difference was not statistically significant [experimental group vs. control group, RR = 1.00 (95% CI: 0.91-1.10), P = 0.960]. The incidence of hypothyroidism [experimental group vs. control group, 11% (118/1 083) (95% CI: 9%-13%) vs. 1% (11/886) (95% CI: 0-2%), RR = 8.56 (95% CI: 4.63-15.80), P < 0.001] and the incidence of hyperthyroidism [experimental group vs. control group, 7% (75/1 083) (95% CI: 5%-8%) vs. 2% (17/886) (95% CI: 1%-4%), RR = 3.27 (95% CI: 1.95-5.46), P < 0.001] in the experimental group were both higher than those in the control group, and the differences were statistically significant. Conclusions:ICI combined with chemotherapy can effectively improve the OS, PFS and disease remission of patients with ES-SCLC, as well as improve the survival of patients with liver metastases. However, there is no benefit in the survival of patients with brain metastases. The incidence of immune-mediated AE to ICI combined with chemotherapy has increased, but the overall safety is good.