In summer, the air temperature on the Tibetan Plateau (referred to as the "Plateau") has the intraseasonal variation characterized by initial warming followed by cooling. Therefore, studying the long-term changes in intraseasonal air temperature will help to deepen the understanding of the long-term air temperature change on the Plateau. Based on the JRA55 and ERA5 reanalysis datasets, this paper analyzes the long-term warming trend of summer air temperatures in the eastern Tibetan plateau from the perspective of intraseasonal evolution, as well as its atmospheric thermodynamic mechanisms. The results show that the warming trend of the summer temperature in the eastern Tibetan plateau is mainly related to three factors: (1) the significantly accelerated warming rate in mid- and late June; (2) the significantly decelerated cooling rate in mid-August; (3) the significantly prolonged duration of the warming period. Thermodynamic diagnostic results indicate that the meridional temperature advection, which climatologically acts as a cooling role, shows a long-term weakening trend, which may be an important cause of the warming of summer temperatures in the eastern Tibetan plateau. It should be noted that while both reanalysis datasets generally reveal the consistent evolution of air temperature over the eastern Tibetan plateau, there are certain differences in descripting the thermodynamic budget equation, with the JRA55 dataset seemingly revealing better diagnostic results.