Two-/three-dimensional (2D/3D) heterojunction-based photodetectors have attracted much attention due to their highly efficient photoelectric conversion driven by the built-in electric field for high-speed photoresponse. However, a large dark current induced by unexpected surface states at the interface between 2D materials and 3D bulks is widely observed in such structures, greatly degrading their optoelectronic performance. Herein, a heterojunction of proton acid HCl treated MXene (H-MXene)/TiO₂/Si via integrating surface and interface engineering is fabricated, which exhibits decreased dark current and improved environmental stability. A feasible strategy to optimize the interface properties between MXene and Si is proposed by an in-situ oxidation process of MXene into TiO₂, resulting in a suppressed dark current as well as high specific detectivity. Benefitting from the enhanced light absorption of MXene on the bulk Si substrate, the photoresponse of as-fabricated devices in the near-infrared region is also elevated. Moreover, the treatment of proton acid HCl on the surface of MXene brings better conductivity and environmental stability due to the decreased layer spacing of MXene, which is further confirmed by both experimental and theoretical methods. This work opens a unique way to comprehensively boost the optoelectronic performance of MXene-based photodetectors.