Deep rock in-situ temperature-preserved coring is important for the exploration and development of deep resources. In addition, understanding the temperature variation laws of the core during coring is fundamental to achieving temperature-preserved coring. In this study, under the coexistence of the core and strata water inside the coring tool, we explore the factors sensitive to the temperature variation of the core during coring and propose suggestions to reduce the unevenness of core temperature. The findings indicate that at a strata temperature of 150 ℃ and a core lifting speed of 2.5 m/s, during process of lifting the passively insulated core to the ground, natural convection occurs within the coring tool due to buoyancy, circulating in a counterclockwise direction. The temperature difference of the core in the axial and radial directions is 21 and 7.7 ℃, respectively, with temperature variation rates of 21 and 308 ℃/m per unit length, respectively. The greatest decrease in temperature is observed at the outer edge of the core bottom. The natural convection of strata water results in significant temperature differences along the axis of the core, exacerbating the unevenness of core temperature. To ensure uniform core temperature, efforts should be made to minimize the space between the core and the inner tube. In addition, the use of water-blocking mechanisms should be facilitated to reduce the ingress of strata water into the coring device. During the coring process, the frequency of active thermal insulation gradually increases as the ambient temperature decreases, thereby reducing the temperature difference between the inner and outer sides of the coring device to suppress the occurrence of natural convection. These research findings have practical implications for achieving deep rock in-situ temperature-preserved coring, providing theoretical and technical guidance for the development of deep resources such as coal, geothermal energy, and oil and gas.