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Nano-zirconium carbide precursor was prepared by hydrothermal method. Nanometer zirconium carbide powder was prepared by carbothermal reduction reaction. The Gibbs free energy and enthalpy change of carbothermic reduction of zirconia were calculated by thermodynamic method. The reaction temperature and reaction mechanism of nanometer zirconia were calculated. The energy and phase changes during the reaction were studied by thermogravimetry and X-ray diffraction. Microstructure observation showed that the precursor was composed of multiple zirconia structures wrapped by a layer of amorphous carbon. This unique structure effectively prevents the agglomeration of the powder and ensures the dispersion of the prepared zirconia. This structure also ensures the dispersion of zirconium carbide powder. Zirconium carbide powder has uniform size and particle size of about 50 nm. Gibbs free energy calculation results show that when the temperature reaches 1656.56 °C, zirconia reacts with C to form CO and ZrC. As the temperature rises, ZrO2 reacts with CO to form CO2 and ZrC. The results of TG-DSC experiments show that the carbothermal reduction reaction starts at about 1100 °C and reaches its peak at 1418 °C. XRD analysis confirmed that ZrC appeared when the temperature reached 1450 °C, and the transformation was basically complete when the temperature exceeded 1600 °C.