Two extreme heat events, caused sequentially by continental high and subtropical high, occurred in Chongqing in the midsummer of 2022. Based on surface observation data and ERA5 reanalysis data, the differences in high temperature characteristics between the two stages dominated by continental high and subtropical high are compared and analyzed. The results show that during the short stage of continental high domination, the heating process was developing with less intensity, high relative humidity and bigger diurnal temperature range. During the long stage of subtropical high domination, the heat event exhibited great extremity, grew severe with pronounced xerothermic characteristics and nocturnal warming. The diagnosis of thermodynamic equation reveals that when the continental high was dominant, diabatic heating and vertical motion jointly contributed to the warming, while when subtropical high set in, diabatic heating and heat advection became the primary and secondary factors for the diurnal warming, and the contribution of vertical motion became insignificant. At night, as the dry adiabatic or super-adiabatic layer at lower level abated and vanished, the warming effect induced by downward motion on the northern side of Yunnan-Guizhou Plateau drastically intensified. The surface thermodynamic difference suggests that the surface latent heat flux decreased and sensible heat flux increased significantly under the domination of subtropical high than under the continental high. The increasing surface sensible heat directly heated the atmosphere, intensively driving up the surface temperature.