Objective To study the mechanism of polymorphism of Hbb gene at single nucleotide polymorphism(SNP)level. Methods Hbb gene was analyzed in 3 aspects,i.e. DNA,RNA and protein polypeptides. Results For the genome DNA,four SNP loci,two T(G) of exon 1,G(A) of exon 2 and A(G) of exon 3,were detected correlating with Hbb d/s haplotype. For the RNA,four SNP loci,corresponding to two T(G) of exon 1,G(A) of exon 2,and A(G) of exon 3,were found correlating with Hbb d/s haplotype. For the protein polypeptide,three interchanges of Cys/Gly,Ser/Ala,Thr/Ala at position 13,20 and 139 were detected correlating with Hbbd and Hbbs haplotypes,which corresponded to two T(G) of exon 1 and A(G) of exon 3,respectively. Conclusion Three interchanges of Cys/Gly,Ser/Ala,Thr/Ala at position 13,20 and 139 might provide the basis for the two haplotypes,Hbbd and Hbbs.