Background: Extensive-stage small-cell lung cancer (ES-SCLC), a type of aggressive tumor known as with limited therapeutic options and poor prognosis in the past decades, had recently been proved curatively effective by the combination of immune checkpoint inhibitor and platinum-based chemotherapy. Nonetheless, it is still worthy and necessary to explore the new treatment pattern considering the rapid disease progression feature of ES-SCLC. Whereupon, this study aims to explore the effectiveness and safety of camrelizumab combined with chemotherapy followed by maintenance camrelizumab and apatinib in the first-line treatment of ES-SCLC. Methods: In this phase II study, 40 patients with pathological diagnosis of ES-SCLC and without receiving prior systemetic therapy are anticipated to be enrolled, and will be dosed camrelizumab (200 mg, iv, q3w) combined with etoposide (80-100 mg/m², iv, q3w, 4-6 cycles) and platinum drugs (selected by the researcher accordingly, iv, q3w, 4-6 cycles), followed by maintenance with camrelizumab and apatinib (250 mg, qd). The primary endpoint is 6-month progress-free survival (6-month PFS) rate while the secondary endpoints are objective response rate (ORR), disease control rate (DCR), progression-free survival, overall survival and safety. Results: Up to January 24, 2024, 31 patients with a median age of 60 years (ranged from 38 to 75 years of age) were enrolled. Among them 28 patients out of 31 were capable for efficacy analysis, of which 23 patients achieved partial response, 3 had stable disease and 2 progressive disease. The ORR and DCR reached 82.14% and 92.86%, respectively. The 6-month PFS rate in evaluable patients was 75.44% and the median PFS was and 7.56 months. The median OS was 15.38 months. During the course of therapy, the grade 3 or worse treatment-related adverse events were hypertension (6.45%), increased ALT level(3.26%), increased AST level(3.26%), increased γ-GT(3.26%)and hypertriglyceridemia (3.26%). Common grade 1-2 adverse reactions included anemia(54.84%), nausea (54.84%), vomiting(45.16%). The treatment was well tolerated and no toxic death occurred. All the adverse events can be controlled and alleviated after symptomatic treatment. Conclusions: Camrelizumab with chemotherapy followed by maintenance camrelizumab plus apatinib showed preliminary efficacy and acceptable safety profile, and might be a promising regimen as first-line treatment in ES-SCLC. Clinical trial information: ChiCTR2000035599.