Abstract: This paper investigated and discussed the evolutionary relations of four histone molecules,H2A,H2B,H3 and H4 with the static accessibilities of protein amino acid residues as an index.The phylogenetic trees of H2A,H2B and H3 have been obtained.The results indicated that protein three-dimensional structure is more reliable as studing protein molecular evolution;in addition,H4 is the most conservative protein in the four histone molecules composing nucleosome.The authors speculate upon that histone H4,as compared with other histones,perhaps has the most important significance both in keeping chromosomal structure and function and in the origin of chromosome.