It has been identified that S-1 is an effective adjuvant treatment for East Asian patients who have undergone a D2 dissection for locally advanced gastric cancer（GC) in the Japanese Adjuvant Chemotherapy Trial of TS-1（S-1) for Gastric Cancer (ACTS-GC) trail , And S-1 has become one of the standard therapies to these patients. But it is still unknown whether it would improve equally or even more to overall survival(OS) and disease free survival(DFS) than S-1 for 1 year compared with S-1 for 6 months. As a result , An further clinical trail is still needed, This trial is designed to investigate the efficacy and safety of S-1 for 6 months versus S-1 for 1 year as adjuvant chemotherapy after D2 resection in patients with gastric cancer.