The electronic structure of LiFePO4, including the energy band, PDOS and popularity analysis was determined by the first-principles based on the density functional theory (DFT), via Nb substituting for Fe or Li with Nb in LiFePO4 supercell. Results show that after Nb doping, the structure is stable and the band gap decreases resulting in the increase of the electronic conductivity and the rate of discharge/recharge, and this can be attributed to the electrons in orbital d, which leads to the increasing of the band near the Fermi level. The bond length of Li-O increases, which benefits the diffusivity of lithium ion. The band gap decreases with more doping amount, and it can influence the diffusivity of lithium ion, especially at Li site. Therefore, it is concluded that the doping content should not be too much.