This is a randomized, open-label, multi-center, phase III trial to evaluate the efficacy and safety of SHR-1210 plus capecitabine and oxaliplatin sequenced by SHR-1210 plus apatinib versus capecitabine and oxaliplatin as first-line therapy in patients with locally advanced or metastatic gastric or gastroesophageal junction (GEJ) adenocarcinoma.

Inclusion Criteria:

• Has histologically- or cytologically-confirmed diagnosis of locally advanced unresectable or mestastatic 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 HER-2 inhibitor). Subjects with previous adjuvant/neo-adjuvant therapy completed more than 6 months can be enrolled.
• Has measurable disease per RECIST 1.1
• 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 known active central nervous system metastatases
• Has received a live vaccine within 4 weeks prior to the first dose of study treatment
• With any acitve autoimmune disease or history of autoimmune disease, including but not limited to the following: hepatititis, 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.
• Has received prior therapy with an anti-PD-1, anti-PD-L1, or anti-CTLA-4 antibody, or a VEGFR inhibitor.
• 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), orventricular arrhythmia which need medical intervention.
• Hypertension and unable to be controlled within normal level following treatment of anti-hypertension agents: systolic blood pressure > 140 mmHg, diastolic blood pressure > 90 mmHg.