Pyroelectric materials are widely investigated for thermal devices. As an efficient standard for evaluation, the pyroelectric figures of merit (FoM) for specific thermal-related applications can clearly represent the performance of voltage responsivity and detectivity. In this paper, six congruent lithium niobate (CLN) single crystals with different ZrO2 doping concentrations were grown by the top-seeded melt growth method including pure CLN. In order to analyze the dielectric and pyroelectric performances, the concentrations, and occupations were extensively studied by ultraviolet and infrared absorption spectra. Our results present an efficient way to improve the FoM of CLN by using zirconia doping. The working temperature of Zr:CLN thermal device can be widened obviously.