This study investigates the optical properties and microstructure of ${\mathrm{Ta}}_2{\mathrm{O}}_5$ film deposited with the glancing angle deposition technique. The tilted nanocolumn microstructure, examined with scanning electron microscopy, induces the optical anisotropy of thin film. The optical properties of thin film are characterized with an inverse synthesis method. Based on the Cauchy model, the dispersion equations of optical constants of film are determined from the transmittance spectra measured at normal and oblique incidence over $400–800\mathrm{nm}$ . The starting values derived with an envelope method quicken the optimization process greatly. The dispersion of the principal indices $N_1$ , $N_2$ , and $N_3$ and the thickness d of thin film are presented statistically. A good agreement between the measured optical properties and theoretical calculation is obtained, which validates the model established for thin film produced by glancing angle deposition.