A novel Tunneling Field Effect Transistor (TFET) photodetector based on silicon on insulator is proposed, which combines a photodiode with TFET to realize photodetection and amplication. The anode pole of the photodiode is tied with the gate of TFET. After illumination, the photogenerated potential of the photodiode controls the channel state and drain current of the TFET photodetector, and converts the light into current. The subthreshold region is used to amplifies the drain current, and the responsivity of the detector is improved obviously. Two dimensional numerical simulations were performed in SILVACO. The P region of the photodiode forms the bottom gate of the TFET through the thinner BOX, which enhances the control of the channel and increases the drain current. The results show that the detector has higher responsivity in weak light. When the light intensity is less than 10 mW/cm², the responsivity of TFET photodetector can exceed 10⁴ A/W. In addition, adjusting the photodiode bias and inserting n⁺ pockets between the source and the channel can also improve the drain current and responsivity of photodetector.