Gastric cancer (GC) is one of the most common malignant tumors with high incidence and mortality in the world. Currently, the alterations of protein glycosylation has been extensively reported during gastric carcinogenesis and cancer progression. In the initial steps of the process of gastric carcinogenesis, Helicobacter pylori (H. pylori) uses glycan to adhere the host mucosa, which leads to the increase of sialyl-Lewis^x level. Further up-regulation of the H. pylori colonization induces sustained inflammation in stomach. In the process of chronic atrophic gastritis and intestinal metaplasia, sialyl-Tn antigen showed a significant up-regulation. Moreover, in GC, the abnormal protein glycosylation emerges in serum and tissue from GC patients as well as GC cell lines, such as down-regulation of core fucosylated N-glycan and up-regulation of β1, 6-GlcNAc branched N-glycan were discovered. It also shows that the altered glycosylation of adhesin contributes to the development of GC. This review summarizes the recent progress of protein glycosylation in GC and the important functions of glycosylation in the carcinogenesis and development. Finally, the application values of the alterations of glycosylation, such as potential biomarker for early diagnosis and drug target designing were discussed.