Abstract: The different roles of the three metal atoms in biology have been studied preliminarily. The model complexes [(C₂H₂X₂)₂Me]ⁿ with central atom Me=Be, Mg, Zn, liganding atoms X = O,S and the charges of the complexes n=+2,0,-2 are studied by SCF-X_α-SW method. The results show that the complexes with different metals have different structures of one-electron eigenvalue and eigenfunctions. The complexes with central atoms Be have highest density of states, highest electron negativity and widely spreaded molecular orbitals nearby Fermi energy levels. The charges of the three metal atoms in the complexes with liganding atoms X=S are quite different. The charges of Mg are biggest, the charges of Be medium, Zn nearly zero. Probably it hints some relation between diffrent roles of the three metal atoms in skin and different charges of the atoms in the sulfur complexes.