A many-mode model which contains the intra-structure of pyrazine ring is presented and applied to the Creutz-Taube ion, a pyrazi ne-bridged mixed-valence compound of ruth-enium. In C-T ion, two Ru4dxz obitals are coupled with one π* obital on the pyrazine bridged ligand. They form linear combination which we lable as bonding (B), nonbonding (N), and antibonding (A) combination. Three many-dimensional potential surfaces are constructed. And the optical absorptions are considered as corresponding to transition between related potential surfaces. The results are more close to experimental data.