A Study of SHR-1210 in Combination With Capecitabine + Oxaliplatin or Apatinib in Treatment of Advanced Gastric Cancer

Inclusion Criteria: * Has histologically- or cytologically-confirmed diagnosis of locally advanced unresectable or metastatic adenocarcinoma of stomach or the esophagogastric junction (GEJ). * Age ≥ 18 years old, male or female. * NO previous therapy for advanced/metastatic disease of GC/GEJ (including HER2 inhibitor). Subjects with previous adjuvant/neo-adjuvant therapy completed more than 6 months can be enrolled. * Has measurable disease per RECIST 1.1. * Life expectancy ≥ 12 weeks. * Eastern Cooperative Group (ECOG) performance status of 0 to 1. * Has adequate organ function. * Females of childbearing potential (FOCBP), who are not surgically sterile or postmenopausal, must conduct pregnancy test (serum or urine) within 7 days before enrollment, and must not be pregnant or breast-feeding women. If the result is negative, she must agree to use adequate contraception during the experiment and 3 months after the last administration of the test drugs. And non-sterilized males who are sexually active must agree to use adequate contraception during the experiment and 3 months after the last administration of the test drugs. Exclusion Criteria: * Has known HER2-positive status. * Has received prior therapy with an anti-PD-1, anti-PD-L1, or anti-CTLA-4 antibody, or a VEGFR inhibitor. * Has known active central nervous system metastases. * Has received a live vaccine within 4 weeks prior to the first dose of study treatment. * With any active autoimmune disease or history of autoimmune disease, including but not limited to the following: hepatitis, pneumonitis, uveitis, colitis (inflammatory bowel disease), hypophysitis, vasculitis, nephritis, hyperthyroidism, and hypothyroidism, except for subjects with vitiligo or resolved childhood asthma/atopy. Asthma that requires intermittent use of bronchodilators or other medical intervention should also be excluded. * Clinically significant cardiovascular and cerebrovascular diseases, including but not limited to severe acute myocardial infarction within 6 months before enrollment, unstable or severe angina, Congestive heart failure (New York heart association (NYHA) class \> 2), or ventricular arrhythmia which need medical intervention. * Hypertension and unable to be controlled within normal level following treatment of anti-hypertension agents(within 3 months): systolic blood pressure \> 140 mmHg, diastolic blood pressure \> 90 mmHg. * Coagulation abnormalities (INR \> 1.5 or APTT \> 1.5×ULN), with bleeding tendency or are receiving thrombolytic or anticoagulant therapy.