Inclusion Criteria:  Male or female patients aged 18 and 75 years old; Signed the informed consent form prior to patient entry; Eastern Cooperative Oncology Group performance status of 0 or 1; Expected Survival Time: Over 3 months; Pathological or cytologically proven extensive-Stage small cell lung cancer(according to Veterans Administration Lung Study Group)and without progression after Cycles 4-6 21-day cycles of first-line Standard chemotherapy(Evaluation was CR /PR/SD based on RECIST1.1); If prophylactic cranial irradiation (PCI) was not planned,informed consent was required to be written between 3 weeks and 5 weeks after day 1 of the last cycle of chemotherapy. If PCI was planned or already performe, informed consent was required to be written between 3 weeks and 8 weeks after day 1 of the last cycle of chemotherapy.  Exclusion Criteria:  Has prior therapy with anti-programmed cell death (PD)-1, anti-PD-L1,anti Cytotoxic T lymphocyte-associated Antigen(CTLA)-4 or other Drugs that target T cells; Has prior therapy with angiogenesis inhibitors,Such as sunitinib, bevacizumab, apatinib, anlotinib; Has active or untreated central nervous system (CNS) metastases and/or cancerous meningitis; Imaging (CT or MRI) shows that tumor invades large blood vessels or the boundary with blood vessels is unclear; 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 allocation ≥1 week; Within the past 2 weeks have used high dose antibiotics; According to the judgement of the researchers, there are other factors that may lead to the termination of the study.