Compared to the conventional silicon-based Double Gate Tunneling Field Effect Transistor (DGTFET), the Si/Ge heterojunction DGTFET shows better electrical performance. Based on Sentaurus TCAD, two types of Si/Ge heterojunction DGTFET with/without pocket structure had been established. The performance of the device was studied by insight into the effects of pocket structure, thickness and doping concentration of the pocket region on the on-state current (Ion), off-state current (Ioff), subthreshold swing (SS), cut-off frequency(fT) and gain bandwidth product (GBW). Through simulation experiments and calculation analysis, it was found that the Ion, Ioff, SS, fT and GBW of Si/Ge heterojunction DGTFET increased with the increase of doping concentration in the pocket region. The thickness of the pocket region had no obvious effect on the device performance. The results of the study provided a good guidance for the optimization of DC and frequency characteristics of the TFET device.