Abstract: The ab initio calculations on models of the three coordinate--Ni₂Ru phosphine thiolato complex （Ni²Ru （mp）₃ （Hmp）（PBu₃ⁿ）₃）are performed, applying the G94W software at Hartree-Fock level and using STO-3G basis set. The electronic structure of the complex, the characteristic of its bonding, the population regularity of the atomic net charges and the factor saffecting the thi-coordinate-Ni structure, etc., were inverstigated. The results show that there is obvious π-bonding interaction between the tri-coordinate-Ni and the Ru atoms in the simplified models. It is this direct Ni-Ru interaction Which could be the main reason for the fonnation of the thi-coordinate-Ni structure. Besides, the Ni（2）maintenance is important to the stability of the molecule of the title complex. Moreover, the electron donating effect of the bridging sulfur atoms also contribute significantly to the stability. The results also indicate that the elec-tion spin densities are predominantly located on Ni（1）center Which should be the active site for further chemical reactions.