Electronic and atomic structures of LiP5, Li3P7 and LiP, which are formed in the process of lithium intercalation into black phosphorus, are systematically studied and analyzed using first-principles ultrasoft pseudopotential method based on the density functional theory (DFT). By caculating the electronic strucrures of these products, we find that the three products are all of semiconductor band structure, of which band gaps are larger than those of black phosphorus, indicating that the electronic conductivity of the black phosphorus is reduced after lithium has been intercalated into it. We simulate the diffusion of lithium ions in the LiP5, Li3P7 and LiP materials using nudged elastic band (NEB) method, and the diffusion activation energy of lithium ions is obtained firstly through the theoretical calculation. Compare with the results of other electrode materials, our results show that the migration energy barriers of lithium ions in LiP5, Li3P7 and LiP are all low. The diffusion coefficient of lithium ions in LiP5 is about 10-4 m2/s and the diffusion channel is one-dimensional. The diffusion coefficient of lithium ions in Li3P7 is approximately 10-7-10-6 cm2/s and the diffusion channel is three-dimensional. The diffusion coefficient of lithium ions in LiP is approximately 10-8-10-5 cm2/s and the diffusion channel is three-dimensional.