LiFe1-xNixPO4/C (x=0.0, 0.1, 0.3, 0.5) cathode materials were synthesized by a carbothermal reduction technique and the effect of Ni2+ substitution on the electrochemical performances were systematically investigated. The results reveal that the cycle performance and electrochemical reversibility of LiFePO4 are remarkably improved with the substitution of Fe2+ ions by Ni2+ ions and LiFe0.9Ni0.1PO4/C demonstrates good electrochemical performances with discharge capacity of 160 mAh·g-1 at a discharge rate of 0.2 C (1 C=170.0 mA·g-1). The improvement of the reversible capacity and the high C-rate performance of LiFePO4 could be attributed to the enhancement of the electronic conductivity and the decrease of the charge transfer resistance. The first-principle calculations were employed to investigate the electronic structures of the LiFe1-xNixPO4/C composites. The Lattice parameters, total energies, density of states have were also studies in details. The results show that the electronic conductivity of the Ni2+-doped materials can be improved to certain extent. LiFe0.875Ni0.125PO4 has the most stable structure, the smallest band gap and the best conductivity