Interface engineering stands out as an effective method for enhancing the performance of photodetectors. This study presents ultraviolet(UV) photodetectors featuring a Gr (2D) /GaN (3D) van der Waals heterojunction, skillfully regulated through interface engineering control. The GaN film efficiently absorbs photons, generating electron-hole pairs promptly separated by the built-in electric field. Photogenerated holes traverse to the Gr side through the tunneling effect, while photogenerated electrons move towards the GaN side. At elevated built-in field levels, high-speed photogenerated carriers undergo impact ionization, leading to a multiplication of the photocurrent. The outcomes highlight the significant influence of lead sulfide quantum dots (PbS QDs) on the light absorption efficiency and photoelectric conversion efficiency of the device. Consequently, the device achieves a remarkable responsivity value of 395.2 A/W and a substantial detectivity value of 4.425×10¹⁵ Jones under 5 μW/cm² light at -2 V. This research contributes to the application of interface engineering technology in Gr-based UV photodetectors, opening possibilities for the preparation of high-performance UV detectors.