Glycosylation, especially N-glycosylation, is a universal post-translational modification in regarding the localization, function, activity of proteins in tissues and cells. The study of the N-glycosylation site is an important prerequisite for understanding the function of sugar chain of the target protein. Among the information related to N-glycosylation, the site of N- glycosylation is the basis for our understanding of its sugar chain function. Besides the application of point mutation in traditional biochemistry, the study of glycosylation sites has also played an important role in the identification of glycosylation sites in N-terminal. LC-ESI-MS/MS are commonly used to identify the N/O-glycosylation sites in the antibodies.