Abstract: The first-principles method is used to study the fine-grained evolution of the electronic structure of a vertical van der Waals heterojunction formed by a single layer of molybdenum disulfide (MoS2) on a 1 to 7 layer hexagonal boron nitride (hBN) substrate, and the characteristics are analyzed. In addition to calculating the influence of the number of hBN layers on the optical properties of heterojunctions, the effect of the number of hBN layers on the optical properties of single-layer MoS₂ is also studied. The calculation results show that the MoS₂/hBN van der Waals heterojunction as a gate dielectric MoS₂ FET can adjust its properties by changing the number of two-dimensional semiconductor hBN layers. The research results provide the necessary theoretical basis for the development of a new generation of MoS₂-based field effect transistors and photodetectors.