The purpose of this study is to evaluate the efficacy and safety of Apatinib Mesylate Tablets combined with docetaxel and S-1 as the first-line treatment of metastatic gastric cancer.

Inclusion Criteria:

1. Age: 18-70 years of age;
2. recurrent or metastatic adenocarcinoma of the stomach or gastroesophageal junction diagnosed by pathology (including histology or cytology);
3. 1 measurable lesions at least should be detected by CT/MRI examination in accordance with the RECIST(Response Evaluation Criteria In Solid Tumors）1.1;
4. had not received other anti VEGFR targeted therapy;
5. ECOG（Eastern Cooperative Oncology Group）PS（Performance Status）:0-2 scores;
6. the expected survival time is more than 3 months;
7. if patient had accepted the chemotherapy, the time from the last chemotherapy should be more than 6 months;
8. the damage caused by other treatments has been restored, and the subjects received radiotherapy or surgery over 4 weeks ago, and the wound has healed completely;
9. the main organ function is normal, which should meet the following criteria: (1) blood routine examination standards should be met: (no blood transfusion within 14 days) A. HB（hemoglobin） = 90g/L, B. ANC(absolute neutrophil count) = 1.5 * 109/L, C. PLT（platelet） = 80 * 109/L; (2) biochemical examination shall comply with the following criteria: A. BIL（bilirubin） <1.25 normal upper limit (ULN), B. ALT（glutamic-pyruvic transaminase） and AST（glutamic-oxalacetic transaminase）<2.5ULN（upper limit of normal）, if subjects have liver metastases, the ALT and AST <5ULN（upper limit of normal）, C. Cr ≤ 1ULN, CCR（creatinine clearance rate） > 50ml/min (Cockcroft-Gault formula);
10. women of childbearing age must have a pregnancy test in 7 days before entering the group (in serum), and the results were negative, and willing to use appropriate contraception during the study period and the last 8 weeks after giving drug test; men should have the surgical sterilization, or adopt the appropriate contraceptive methods during the test and the last 8 weeks after giving drug test;
11. participants is willing to participate in this study, sign the informed consent, have good compliance, cooperate with follow-up.

Exclusion Criteria:

1. Suffering from other malignant tumors previously or at the same time, with the exception of cured skin basal cell carcinoma and cervical carcinoma in situ;
2. Patients have used the paclitaxel class and / or S-1 as the adjuvant therapy in 2;
3. have been confirmed to be allergic to docetaxel, 5-fluorouracil, apatinib and / or its accessories;
4. the blood pressure of patients with hypertension cannot be reduced to the normal range by the antihypertensive drugs (systolic pressure >140 mmHg, diastolic pressure >90 mmHg);
5. patients are suffering from severe cardiovascular disease: the II level of myocardial ischemia or myocardial infarction, poor control of the arrhythmia (including QTc(corrected QT interval) prolongation of male > 450 ms, of female > 470ms ); and patients have III-IV grade of cardiac insufficiency, or left ventricular (LVEF) < 50% shown by echocardiography according to the NYHA(New York Heart Association) standard;
6. patients are positive of urine protein (urine protein detection 2+ or above, or 24 hours urine protein quantitative >1.0g);
7. have a variety of factors that affect oral drugs (such as difficulty in swallowing, nausea, vomiting, chronic diarrhea and intestinal obstruction, etc.);
8. patients have a clear tendency with gastrointestinal bleeding, including the following situation: local active ulcerative lesions, and fecal occult blood (+ +); with melena and hematemesis history in 2 months; and patients with fecal occult blood (+) and unresected gastric primary tumor; patients with the risk of bleeding should take the gastroscopy test, if it is the gastric cancer, and researchers believe that may results in massive digestive tract hemorrhage;
9. coagulation dysfunction (INR(international normalized ratio)>1.5, APTT(activated partial thromboplastin time)>1.5 ULN), with bleeding tendency;
10. patients with a history of psychotropic substance abuse and unable to give up or have mental disorders;
11. Patients who participated in other clinical trials within 4 weeks;
12. have received the VEGFR inhibitors, such as sorafenib and sunitinib;
13. according to the researcher's judgment, there are other accompanying disease endangering the patient's safety or affect the patient to complete the study.
14. patients with central nervous system metastasis;
15. pregnant or lactating women;
16. the researchers consider those who were not suitable for inclusion.