The relation among electronic structure, chemical bond and thermoelectric property of Ca3 Co2 O6 and Ni-doped was studied by density function theory and discrete variation method(DFT-DVM). The results indicate that the highest valence band (HVB) and the lowest conduction band(LCB) are mainly attributed to Co3 d, Ni3 d and O2 p atomic orbitals. The property of a semiconductor is shown from the gap between HVB and LCB. The gap of Ni-doped one is less than that of Ca3 Co2 O6. The non-metal bond or ceramic characteristic of Ni-doped one is weaker than that of Ca3 Co2 O6, but the metal characteristics of Ni-doped one are stronger than those of Ca3 Co2O6. The thermoelectric property should be improved by adding Ni element into the system of Ca3 Co2 O6.