Background: The treatment mode of small cell lung cancer (SCLC) is mainly based on the comprehensive treatment of chemotherapy and radiotherapy. IMpower133 study, suggesting that immune checkpoint inhibitors combined with chemotherapy first-line treatment for advanced SCLC may bring new research directions of clinical benefit. Previous study suggested that the combination of anti-PD-1 antibody camrelizumab and VEGFR-2 inhibitor apatinib significantly improved antitumor effects. The aim of this study was to evaluate the efficacy and safety of camrelizumab combined with chemotherapy (irinotecan combined with platinum) followed by camrelizumab combined with apatinib in the first-line treatment of SCLC. Methods: Extensive-stage small cell lung cancer patients were enrolled in this single-center, single-arm study. During the induction treatment phase, Patients received camrelizumab (200mg q3w), irinotecan (65 mg/m2, q3w) and platinum (cisplatin: 30 mg/m2, carboplatin: AUC=4̃5), after 4-6 cycles, the patient entered the maintenance phase, and then patients received camrelizumab combined with apatinib until disease progression or unacceptable toxicity. Treatment efficacy was assessed every 3 cycles (6 weeks). The primary endpoint is progression-free survival (PFS). Secondary endpoints are objective response rate (ORR), disease control rate (DCR), duration of response (DoR) and overall survival (OS), which are based on RECIST 1.1. Results: At data cut-off (Jan 10, 2022), 20 extensive-stage SCLC patients were enrolled in the study, of which 18 patients were evaluable. Median age was 64 years, male accounts for 85.0% (17/20). Median follow-up was 5.0 months (range 0.4̃17.6 months). Of 18 evaluable patients, no one achieved complete response Partial response was achieved by 17 (94.4%) patients and stable disease exhibited by 1 (5.6%) patient. The ORR and DCR were 94.4% and 100%, respectively. mPFS and mDoR have not been reached. In terms of adverse events (AEs), reactive cutaneous capillary hyperplasia (RCCEP) was observed in 10 (47.6%) patients 10 patients. Grade III-IV AEs were observed in 7 (35.0%) patients with neutropenia, thrombocytopenia, hemoglobin reduction, leukopenia, rash. The rest were grade I-II AEs. Conclusions: The treatment in this study showed impressive ORR and DCR, and acceptable toxicity, and may be a promising method as a first line treatment. Clinical trial information: NCT04453930.