Inclusion Criteria:
1.Ability to understand and voluntarily sign a written informed consent form (ICF), which must be signed before the specified study procedures required for the study are performed； 2.18 to 75 years old (at the time of inform consent obtained)； 3.Have an Eastern Cooperative Oncology Group (ECOG) performance status of 0-1； 4.Have a life expectancy of at least 3 months； 5.Have histologically- or cytologically-confirmed diagnosis of Extensive Stage SCLC； 6.Had not received previous systemic therapy; Or ES-SCLC patients who had received definitive chemoradiotherapy for limited-stage small-cell lung cancer but had disease progression \> 6 months earlier; 7.Have measurable disease based on Response Evaluation Criteria in Solid Tumors (RECIST) 1.1 assessed by investigator； 8.Be able to provide formalin fixed, paraffin-embedded (FFPE) tumor tissue obtained from either a core or excisional tumor biopsy； 9.Have adequate organ function； 10.All female and male subjects of reproductive potential must agree to use an effective method of contraception, as determined by the Investigator, during and for 120 days after the last dose of study treatment；
Exclusion Criteria:
1. Active malignancies within the past 5 years, with the exception of tumors in this study and cured local tumors；
2. Received palliative local treatment, non-specific immunomodulatory treatment within 2 weeks prior to the first dose; and Chinese herbal medicine or traditional Chinese medicinal products with anti-tumor indications within 1 weeks prior to the first dose；
3. Subjects who received any prior treatments targeting the mechanism of tumor immunity；
4. Subjects who received any prior anti-angiogenic therapy；
5. Tumor surrounds important blood vessels or has obvious necrosis, cavitation, or invades surrounding important organs and blood vessels；
6. Active autoimmune disease requiring systemic treatment within 2 years prior to the start of study treatment；
7. Symptomatic metastases of the central nervous system；
8. Presence of clinically symptomatic pleural effusion, pericardial effusion, or ascites requiring frequent drainage；
9. History of perforation of the gastrointestinal tract and/or fistula, history of gastrointestinal obstruction (including incomplete intestinal obstruction requiring parenteral nutrition), extensive bowel resection (partial colectomy or extensive small bowel resection, complicated by chronic diarrhea) within 6 months before the first study drug administration；
10. Has known active Hepatitis B (e.g., HBsAg reactive) or Hepatitis C (e.g., HCV RNA \[qualitative\] is detected);
11. History of myocardial infarction, unstable angina, cardiac or other vascular stenting, angioplasty, or surgery within 12 months prior to day 1 of study treatment;
12. Severe infection within 4 weeks prior to the first dose, including but not limited to comorbidities requiring hospitalization, sepsis, or severe pneumonia; active infection that has received systemic anti-infective therapy within 2 weeks prior to the first dose (excluding antiviral therapy for hepatitis B or C)；
13. Concurrent enrollment in another clinical study, unless it is a noninterventional clinical study or the follow-up period of the interventional study is more than 4 weeks from the last dose of the prior clinical study or more than 5 half-lives of the prior study drug, whichever is shorter.
