In this paper, a garnet-related type Li7La3Zr2O12 material is synthesized by using a solid-state method. Then, the obtained Li7La3Zr2O12 is investigated by X-ray diffraction method and field emission scanning electron microscopy. The prepared Li7La3Zr2O12 material is first used as the lithium thermal electrolyte for its good ionic conductivity and safety at 550 degrees C. Compared with LiCI-LiBr-LiF molten salt electrolyte, the lithium thermal batteries using Li7La3Zr2O12 material as the electrolyte have longer discharge time and higher melting point, resulting an increasing of the utilization rate of active substance by 20% at 550 degrees C under 80 mA/cm(2). In addition, there was no Li7La3Zr2O12 electrolyte overflowing during this discharge process, and which is beneficial to prolong the lithium thermal battery life and improve the lithium battery safety.