Based on a non-collinear magnetic structure calculation, the magnetism, energy gap, and electronic structures of the triangular lattice antiferromagnetic delafossite CuFeO2 were investigated by density functional theory (DFT) within the generalized gradient approximation (GGA) approach. By producing three types of magnetic configurations including ferromagnetic (FM), frustrated triangular non-collinear antiferromagnetic (FAFM), and up-up-down-down collinear antiferromagnetic (↑↑↓↓AFM) ordering, a full optimization of the lattice parameters and internal coordinates was performed for the low temperature hexagonal structure. The calculations show that the up-up-down-down spin arrangement plays an important role in the formation of the band gap, the decrease in total energy and the increase in magnetic moment. Since a small difference exists between the total energy of the FAFMand ↑↑↓↓AFM phase, the ↑↑↓↓AFMeasily undergoes a phase transition to the FAFMstate when an external magnetic field is applied. Additionally, the electronic densities of states (DOS) in the ↑↑↓↓AFMphase qualitatively agrees with the results of X-ray emission spectra, that is, the Fe ion is in a high-spin state with the spectral weight of the Fe 3d spin-up band centered slightly below the Cu 3d but above the O 2p bands. Analysis with ligand field theory also indicates that the empty orbital of the Fe 3d spin-down provides a chemical environment favorable for ferroelectric polarization.