Abstract: In order to study the electrical aging characteristics of main insulation of large generator stator bar, the thermally stimulated current(TSC) was used to research the main insulation properties of vacuum pressure impregnating(VPI), the formation mechanism of TSC peak was analyzed, and the characteristic parameters of the TSC peak were calculated. Fourier transform infrared spectroscopy(FTIR) was used to analyze the group changes of the adhesive contained in the insulating material, and scanning electron microscopy(SEM) was used to observe the changes in material morphology in the microscopic state. The test results show that the TSC spectrum of VPI main insulation is a double-peak curve caused by turning polarization and interface polarization in measured range of −40~ 120 ℃, and the peak temperatures are at around −5 ℃ and 70 ℃. With the increase of electrical aging time, the activation energy of turning polarization peak decreases slightly, the interface polarization peak increases obviously, and the amplitude and release charge of each peak curve increase to different degrees. The results of this study lay the foundation for analyzing the aging mechanism of the main insulation of stator bar by using the TSC method.