A Study of TQB2450 or Placebo Combined With Anlotinib, Etoposide and Carboplatin Versus Etoposide and Carboplatin in Subjects With Extensive Small Cell Lung Cancer (ETER701)

Inclusion Criteria: * 1\. Pathologically confirmed extensive small cell Lung cancer; 2. Has not received systematic treatment for extensive small cell lung cancer; 3. Has received radiotherapy and chemotherapy for limited stage SCLC must have received radical treatment, and has at least 6 months of no treatment interval from the last treatment to the diagnosis of extensive SCLC; 4. Has measurable lesion based on Response Evaluation Criteria in Solid Tumors (RECIST) version 1.1; 5. 18 and 75 years old; Eastern Cooperative Oncology Group (ECOG) performance status of 0 or 1, life expectancy≥ 12 weeks; 6. Adequate organ system function; 7. Male or female subjects should agree to use an adequate method of contraception starting with the first dose of study therapy through 6 months after the last dose of study (such as intrauterine devices , contraceptives or condoms) ; No pregnant or breastfeeding women, and a negative pregnancy test are received within 7 days before the randomization; 8. Understood and signed an informed consent form. Exclusion Criteria: * 1\. Has prior therapy with anlotinib, anti-programmed cell death (PD)-1, anti-PD-L1 or other immunotherapy against PD-1/PD-L1; 2. Has central nervous system metastasis and/or cancerous meningitis; 3. Has diagnosed and/or treated additional malignancy within 5 years prior to randomization. Exceptions include cured basal cell carcinoma of skin and carcinoma in situ of cervix; 4. Has multiple factors affecting oral medication, such as inability to swallow, post-gastrointestinal resection, chronic diarrhea and intestinal obstruction, etc; 5. Has uncontrollable pleural effusion, pericardial effusion, or ascites requiring recurrent drainage procedures; 6. Has spinal cord compression which was not cured or relieved through surgery and/or radiotherapy, or diagnosed spinal cord compression after treatment showed no clinical evidence of disease stabilization prior to randomization ≥1 week; 7. Imaging (CT or MRI) shows that tumor invades large blood vessels or the boundary with blood vessels is unclear; 8. Within 2 months prior to initial administration, subjects with evidence or history of bleeding tendency, regardless of severity; A history of hemoptysis (defined as blood bright red or 1/2 teaspoon) or an unhealed wound, ulcer, or fracture in the 2 weeks prior to initial administration; 9. Has adverse events caused by previous therapy except alopecia that did not recover to ≤ grade 1; 10.Has major surgical procedure、biopsy or obvious traumatic injury within 28 days before randomization; 11. Has arterial or venous thromboembolic events occurred within 6 months, such as cerebrovascular accident including transient ischemic attack, deep vein thrombosis and pulmonary embolism; 12.Has drug abuse history that unable to abstain from or mental disorders; 13. Has any severe and/or uncontrolled disease; 14. Has vaccinated with vaccines or attenuated vaccines within 4 weeks prior to first administration.; 15. Severe hypersensitivity occurs after administration of other monoclonal antibodies; 16. Active autoimmune diseases requiring systemic treatment occurred within 2 years prior to first administration ; 17. Immunosuppressive therapy with immunosuppressive agents or systemic or absorbable local hormones (dosage \> 10 mg/day prednisone or other therapeutic hormones) is required for the purpose of immunosuppression, and is still in use for 2 weeks after the first administration; 18. Has participated in other anticancer drug clinical trials within 4 weeks; 19. According to the judgement of the researchers, there are other factors that may lead to the termination of the study.