Optimal recording wavelength for maximum diffraction efficiency of thermal fixing in ${\mathrm{LiNbO}}_3\text{:}\mathrm{Fe}$ crystal is investigated. Holographic gratings are recorded using three typical recording wavelengths including 488, 514, and $633\mathrm{nm}$ . Optimal switching from recording to thermal fixing is taken into consideration. The fixed holograms are developed by an original recording setup. Diffraction efficiencies of recording and thermal fixing are measured by a two-wave coupling technique. The theoretical and experimental results are analyzed and compared. With a blue beam, the nonvolatile hologram with maximum fixing efficiency is achieved. This work can obtain high persistent diffraction of the nonvolatile holographic storage in ${\mathrm{LiNbO}}_3\text{:}\mathrm{Fe}$ crystals.