N-glycosylation is one of the most prevalence protein post-translational modifications which is involved in many physiological and pathological processes. N-glycosylation site occupancy is a physiological feature of glycoproteins and mainly contributes N-glycan macroheterogeneity. The degree of N-glycosylation site occupancy by itself correlates with the severity of the disease. Currently the technical obstacles have restricted research into the regulation and functions of this heterogeneity.