Spectral terms and J-spectral multiplet of low-spin 4f105d configuration of Er3+ were obtained with the method of ligand field theory. According to the selection rules for dipole transitions, the excitation spectra of Er3+ doped in LiYF4 in vacuum ultraviolet region (120～160 nm) of the spectrum were theoretically interpreted by applying the crystal field model, and the six bands were assigned to the spin-allowed transitions from the ground state (4I15/2) to J-spectral multiplet of low-spin 4f105d configuration of Er3+ion. Spectral terms and J-spectral multiplet of low-spin 4f105d configuration of Er3 + were obtained with the method of ligand field theory. According to the selection rules for dipole transitions, the excitation spectra of Er3 + doped in LiYF4 in vacuum ultraviolet region (120-160 nm) of the spectrum were theoretically interpreted by applying the crystal field model, and the six bands are assigned to the spin-allowed transitions from the ground state (4I15 / 2) to J-spectral multiplet of low-spin 4f105d configuration of Er3 + ion.