As a common carbonate mineral, calcite is formed in various geological environments and is widely distributed on the earth. It can change into different phase states with the temperature and pressure change in the deep earth. Its physicochemical properties under different conditions can be of certain guiding significance for understanding the deep carbon cycle of the earth. Due to the decomposition of calcite near 1 164 K, there are relatively few studies on the phase transition of calcite at high temperatures, especially the phase transition from CaCO3-Ⅰ to CaCO3-Ⅳ, which needs more experimental data. In this study, the behavior of calcite at different temperatures was studied by high-temperature Raman (298～1 323 K) and XRD (298～1 223 K) under the CO2 gas stream. High-temperature Raman experiment shows that, with the increase in temperature, the Raman peak obviously moves to the low frequency, the half-height width of the peak gradually increases, and the peak intensity decreases. The Raman shift of 276 cm-1 gradually moves to the lower frequency with increasing temperature. When the temperature rises to 973 K, the Raman shift appears abnormal behavior and moves to 265 cm-1. The frequency remains unchanged in the range of 1 023~1 223 K. When the temperature rises to 1 248 K, it moves to 266 cm-1 and remains unchanged between 1 248 and 1 298 K. Th Raman shift of 706 and 1 430 cm-1 also behavior abnormally near 1 223 K. The abnormal temperature of the Raman shift is speculated to be related to the phase transition of CaCO3-Ⅳ to CaCO3-Ⅴ, which is very close to the phase transition temperature reported by previous research. High-temperature XRD experiments indicate that, with the increase in temperature, some diffraction peaks move to a lower angle, some diffraction peaks move to a high angle, and some adjacent diffraction peaks merge and gradually separate. The peak (211) disappears near 1 123~1 173 K, which is speculated to be related to the phase transition from CaCO3-Ⅰ to CaCO3-Ⅴ. The a-axis of calcite shows negative thermal expansion, and the c-axis shows positive thermal expansion. The thermal expansion equation fitted the cell parameters at different temperatures, and the thermal expansion coefficientα0(a) is -0.60(2)×10-5/K, α0(c) is 2.42(4)×10-5/K, and α0(V) is 1.21(2)×10-5/K. However, there was no obvious change in the XRD pattern near 1 000 K. That is, no CaCO3-Ⅳ was found.