Inclusion Criteria:  1. Extensive stage small cell lung cancer proved by pathology. 2. Extensive small cell lung cancer does not receive systematic treatment. 3. limited SCLC patients have received radiotherapy and chemotherapy for more than 6 months. 4. patients have measurable lesions according to RECIST version 1.1. 5. Male or female who is 18 to 75 years old. 6. ECOG PS 0 or 1. 7. Life expectancy is more than12 weeks. 8. Appropriate organ system function. 9. hyroid-stimulating hormone is ULN or less (If T3 and T4 is normal, he still meets the Inclusion Criteria even the abnormal TSH. ) 10. Take proper contraceptive measures. 11. Subjects voluntarily participate in this study and sign the informed consent.  Exclusion Criteria:  1. Previous treatment with apatinib, anti-programmed cell death (PD-1), anti-PD-1, or other PD-1/ PD-L1 immunotherapy. 2. Cancer meningitis. 3. patients had been diagnosed and/or treated for other malignancies within 5 years prior to enrollment, except for cured basal cell carcinoma of the skin and carcinoma in situ of the cervix. 4. There are many factors affecting oral medication, such as inability to swallow, post-gastrointestinal resection, chronic diarrhea, intestinal obstruction, etc.. 5. Uncontrollable pleural effusion, pericardial effusion or ascites, requiring repeated drainage. 6. Patients with spinal cord compression who were not cured or relieved by surgery and/or radiotherapy, or who were diagnosed with spinal cord compression after treatment and without clinical evidence of stable disease ≥1 week before enrollment; 7. Patients with hypertension who cannot be well controlled by oral antihypertensive therapy, suffer from myocardial ischemia or myocardial infarction of grade I or above, arrhythmias of grade I or above , or cardiac insufficiency; 8. Subjects had signs of bleeding, hemoptysis, or a history of unhealed wounds, ulcers, fractures within 2 months prior to initial administration. 9. The adverse events caused by previous treatment did not completely recover. 10. Patients with major surgery or obvious traumatic injury within 28 days before enrollment; 11. Occurred arterial or venous thromboembolism events within 6 months. 12. People with a history of drug abuse or mental disorders. 13. Suffering from a serious and/or uncontrollable disease; 14. Vaccination or attenuated vaccine received within 4 weeks. 15. Severe allergies that require treatment with other monoclonal antibody drugs; 16. Active autoimmune disease requiring systemic treatment within 2 years prior to the first administration; 17. Immunosuppressive therapy with systemic or absorbable local hormones and continued for 2 weeks after the first dose; 18. Participate in other anticancer drug clinical trials within 4 weeks; 19. In the investigator's judgment, there are other factors that may have led to the termination of the study.