In previous studies, we found that POF (A combination of oxaliplatin, fluorouracil and Paclitaxel) regimen appears to be of good efficacy and is well tolerated in patients with advanced gastric cancer. Apatinib is an orally antiangiogenic agent. It was approved and launched in China in 2014 as a 3rd-line treatment for patients with advanced gastric cancer. Therefore, investigators initialize this dose escalation phase I study to explore the safety of combination of apatinib and POF as first-line treatment for advanced gastric cancer. Investigators will analyze the maximum tolerated dose (MDT) and dose-limiting toxicity (DLT) of apatinib in this study.