In this work, LaNbO4 polycrystalline with monoclinic structure was prepared by traditional high-temperature solid-state reaction method. Its structure was determined by X-ray diffraction and its unit cell parameters were obtained with Rietveld refinement method. Its luminescence properties including excitation, emission spectrum as well luminescence lifetime were characterized in experiment. Besides, a systematic theoretical calculation based on the density function theory methods was performed on LaNbO4. The calculated band gap is in good agreement with that obtained in experiment. A comparison of the calculated and experimental refractive index and reflectivity between LaNbO4, YNbO4 and GdNbO4 was made. All the obtained results provide an essential understanding of LaNbO4.