Abstract: In response to the application demands for high-sensitivity and high-detectivity photodetectors, this paper has designed and constructed an In₂Se₃/WSe₂ van der Waals heterojunction. The electronic structure and optical properties of this heterojunction have been systematically investigated, and on this basis, a polarization-sensitive photodetector has been developed. Through density functional theory calculations and molecular dynamics simulations, combined with optical absorption and photodetector performance analyses, the band structure, thermal stability, charge transfer mechanism, and photoelectric characteristics of the heterojunction have been comprehensively studied. The findings reveal that the In₂Se₃/WSe₂ heterojunction exhibits an indirect bandgap of 0.7 eV and a typical type-II band alignment, and it can maintain good dynamic stability at room temperature. Interface charge transfer analysis indicates that there is a significant charge separation at the heterojunction interface, and an internal electric field is formed, effectively suppressing carrier recombination. Optical absorption characteristic tests show that the absorption coefficient of this heterojunction in the ultraviolet and visible light regions is significantly higher than that of monolayer materials, and the absorption edge is extended to the main energy range of the solar spectrum. Photodetector performance tests demonstrate that the heterojunction has a polarization-sensitive extinction ratio as high as 85 under a photon energy of 2.0 eV, and the carrier mobility exhibits obvious anisotropy in different directions. In summary, the In₂Se₃/WSe₂ heterojunction, with its unique band structure, excellent thermal stability, efficient carrier separation mechanism, and outstanding polarization sensitivity, shows broad application prospects in the field of broadband photodetection.