In this paper, ab initio calculations of the iron-sulfur protein model complexes have been completed on Fe_2S_2(SH)_2~(n-) and Fe_4S_4(SH)_4~(n-)(n=2, 3). The results indicate that the occupied terminal sulfur characteristic orbitals are found in the front orbital site and the energy levels of the occupied Fe 3d-like orbitals appear internally below the S-H bonding orbitals in the valence band. Although the energy sequence is different from what was reported in literature, our results are in agreement with the relevant experimental facts. We have discussed the reason that variations of the active sites are produced by various oxidation levels. The action mechanism of the Fe-S proteins as electron carriers in the biological processes is also explored preliminarily. In this paper, ab initio calculations of the iron-sulfur protein model complexes have been completed on Fe_2S_2 (SH) _2 ~ (n-) and Fe_4S_4 (SH) _4 ~ (n -) (n = 2, 3) indicate that the occupied terminal sulfur characteristic orbitals are found in the front orbital site and the energy levels of the occupied Fe 3d-like orbitals appear internally below the SH bonding orbitals in the valence band. We have discussed the reason that variations that the of the variations of the active sites are produced by various oxidation levels. The action mechanism of the Fe-S proteins as electron carriers in the biological processes is also explored preliminarily.