The study is to investigate the efficacy of Apatinib as maintenance therapy after first fine treatment in patients with advanced or metastatic adenocarcinoma of stomach or gastroesophageal junction through progression-free survival(PFS). Apatinib will be given to patients who have received first-line chemotherapy with an efficacy assessment of stable disease(SD), complete response(CR), or partial response(PR) after 4 cycles. Patients were randomly assigned to 750mg group or 500mg group continually until disease progression or intolerable toxicity or patients withdrawal of consent, and the sample size is 40 individuals.