As shown in Figure 1A , the current 17 HA subtypes were concentrated in two evolutionary groups. One large group, represented by H1 and H5, contained H2, H6, H8, H9, H11, H12, H13 and H16; Another large group was represented by H3, and contained H4, H7, H10, H14 and H15. Although each subtype of HA had a lower similarity to each other and the distribution of the glycosites differed in sequential numbering, we found that the sequence alignment of all HA subtypes indicated that partial glycosites appeared in similar domains. Furthermore, the structure alignment of available HAs also showed that various HA subtypes had a highly conserved structure, and the distribution of glycosites was also regular ( Figure S2 ).