In order to explore the damage mechanism of the total dose ionizing (TID) effect of SiGe HBT is explored by using three-dimensional simulation tool of semiconductor device (TCAD). In the simulation, the trapped charge defects are introduced in different location of oxidation in SiGe HBT to simulate the TID. Then the degradation characteristics of the forward Gummel characteristic and the reverse Gummel characteristic of the device are analyzed, and the TID damage law of SiGe HBT is obtained. Finally, the simulation results are compared with the 60Co γ irradiation test. The results show that the trapped charges introduced by TID irradiation in SiGe HBT devices mainly affects the Si/SiO2 interface near the pn junction, causing changes in the depletion region of the pn junction and increasing carrier recombination. Eventually, the base current increases and the gain decreases. The trapped charge generated in the EB Spacer oxide layer mainly affects the forward Gummel characteristics, and the trapped charge in the LOCOS isolation oxide layer is the main factor causing the degradation of the reverse Gummel characteristics. The total dose effect damage law of SiGe HBT obtained by numerical simulation analysis is in good agreement with the conclusions of 60Co γ irradiation experiments under different biases.