Inclusion Criteria:
* Signed the Informed Consent Form
* Ages: 18-75 Years (concluding 18 and 75 Years)
* Pathologically confirmed gastric/gastroesophageal junction adenocarcinoma, and meets one of the following conditions: invasion of adjacent organs such as colon, tail of pancreas and spleen; localized peritoneal metastasis; positive exfoliative cytology of ascites; class I, class II, part of class III and very few class IV stage IV gastric adenocarcinoma according to biological behavior; N3; extensive or fused lymph node metastasis; Krukenberg tumor; Liver metastasis limited to one lobe, less than 5cm in diameter, isolated abdominal aortic metastasis, etc;
* Untreated(e.g. radiotherapy, chemotherapy, target therapy and immunotherapy)
* Life expectancy greater than 3 months
* ECOG(Eastern Cooperative Oncology Group) :0\~1
* Sufficient organ and bone marrow functions as follows:
1. Absolute Neutrophil Count (ANC) ≥1.5×109/L, White Blood Cell≥3.5×109/L;
2. Platelet Count of ≥100×109/L;
3. Hemoglobin≥90g/L;
4. Total Bilirubin (TBIL) ≤1.5 x ULN;
5. ALT and AST\<2.5 x ULN, GPT≤1.5×ULN; If there is liver metastasis, then ALT and AST\<5.0 x ULN, GPT≤3.0×ULN;
6. Serum Creatinine (SCr) ≤1.0×ULN;
7. Endogenous creatinine clearance rate \> 60ml / min (Cockcroft Gault formula);
* No severe dysfunction of heart, lung and liver; No jaundice and gastrointestinal obstruction; No acute infection
* Not participating in other clinical trials 4 weeks before and during the treatment
Exclusion Criteria:
* Known HER-2 positive
* Distal metastasis to lung, brain, and bone
* Have received operation on the stomach
* A history of other malignancies within 5 years prior to inclusion, except for cervical carcinoma in situ, basal or squamous cell skin cancer
* Patients with any active autoimmune disease or a documented history of autoimmune disease within 4 weeks prior to enrollment
* Previously received allogeneic bone marrow transplantation or organ transplantation
* Known hypersensitivity to any of the study drugs or excipients
* Hypertension that is not controlled by the drug, and is defined as: SBP ≥150 mmHg and/or DBP ≥90 mmHg
* International normalized ratio (INR) \> 1.5 or partially activated prothrombin time (APTT) \> 1.5 × ULN
* Poorly controlled diabetes before enrollment
* Clinically significant electrolyte abnormalities judged by researchers
* With any diseases or conditions that affected drug absorption, or the patient could not take drugs orally
* 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; Congestive heart failure, New York Heart Association (NYHA) grade \> 2; ventricular arrhythmia requiring drug treatment; LVEF (left ventricular ejection fraction) \< 50%
* Active infection or serious infection that is not controlled by drug (≥CTCAE v5.0 Grade 2）
* History of clinically significant hepatic disease, including, but not limited to, known hepatitis B virus (HBV) infection with HBV DNA positive (copies ≥1×104/ml); known hepatitis C virus infection with HCV RNA positive (copies ≥1×103/m)
* Women who are pregnant or lactating
* Urinary protein ≥ ++, and the 24-hour urine protein quantification is greater than 1.0 g
* Have any other disease, metabolic disorder, physical examination anomaly, abnormal laboratory result, or any other conditions which, according to judgement of the investigator, renders the patient inappropriate for using of the investigational product or may affect interpretation of study results
* Patients considered unsuitable for inclusion in this study by the investigator.
