Inclusion Criteria:  Pathologically determined unresectable advanced gastric or gastroesophageal junction adenocarcinoma; 18-75 years old (including 18 and 75 years old); No previous anti-tumor treatment for metastatic diseases; HER2 negative; Eastern Cooperation Oncology Group (ECOG) performance status of 0-1; Life expectancy ≥ 3 months; At least one measurable lesion according to RECIST version 1.1; Adequate organ and bone marrow functions:  Absolute neutrophil count≥1.5x10^9/L; Platelet count≥100x10^9/L; Hemoglobin≥9g/dL; Serum bilirubin≤1.5x the upper limit of normal(ULN); Alanine aminotransferase(ALT) and aspartate aminotransferase(AST)≤1.5x ULN; Serum creatinine≤1.5x ULN; Endogenous creatinine clearance rate ≥ 50ml / min;  Women of childbearing age need to take effective contraceptive measures.  Exclusion Criteria:  Previous treatment with vascular endothelial growth factor receptor (VEGFR) inhibitors or previous use of immune checkpoint inhibitors; Other malignant tumors in the past 5 years, except for skin basal cell or squamous cell carcinoma after radical surgery, or cervical carcinoma in situ; There was central nervous system (CNS) metastasis or previous brain metastasis before enrollment; Patients with autoimmune diseases or history of autoimmune diseases within 4 weeks before enrollment; Previously received allogeneic bone marrow transplantation or organ transplantation; Uncontrolled malignant ascites; Participated in other unapproved or unlisted drug clinical trials in China within 4 weeks before enrollment, and received corresponding experimental drug treatment; Cardiovascular disease, including unstable angina or myocardial infarction, occurred within 6 months before the start of study treatment; Subjects allergic to the study drug or any of its adjuvants; International normalized ratio (INR) > 1.5 or partially activated prothrombin time (APTT) > 1.5 × ULN； The researchers judged clinically significant electrolyte abnormalities; At present, the patient has hypertension that cannot be controlled by drugs, which is specified as: systolic blood pressure ≥ 140 mmHg and / or diastolic blood pressure ≥ 90 mmHg; Patients currently have poorly controlled diabetes (fasting glucose level is greater than CTCAE grade 2 after regular treatment); Patients with dysphagia, active peptic ulcer, intestinal obstruction, active gastrointestinal bleeding, peptic perforation, malabsorption syndrome or uncontrolled intestinal inflammatory diseases; Any disease or state affecting drug absorption before enrollment, or the patient cannot take oral medication; Patients with obvious evidence of bleeding tendency or medical history within 3 months before enrollment, hemoptysis or thromboembolism within 12 months; Cardiovascular diseases with significant clinical significance, including but not limited to acute myocardial infarction, severe / unstable angina pectoris or coronary artery bypass grafting within 6 months before enrollment; Ventricular arrhythmia requiring drug treatment; Congestive heart failure ≤New York Heart Association (NYHA) class 2; LVEF < 50%; Active or uncontrolled severe infection ≥ grade 2 according to National Cancer Institute Common Toxicity (NCI-CTC) criteria; With positive urine protein and 24-hour urinary protein content>1g; Known human immunodeficiency virus (HIV) infection; known history of clinically significant liver disease, including viral hepatitis; Pregnant (positive pregnancy test before medication) or lactating women; Complications require long-term immunosuppressive treatment, or systemic or local use of immunosuppressive corticosteroids (> 10mg / day prednisone or other therapeutic hormones); By judgment of the investigator, there are concomitant diseases that seriously endanger the safety of the patient or affect the completion of the study.