The stability of ZnSe/graphene heterojunction structure, interface interactions, interlayer charge transfer, Schottky contact type, and the influence of external electric field were studied in this paper by first principles plane wave ultra soft pseudo-potential method based on density functional theory. The results demonstrate that the heterojunction is easy to form because of its less lattice mismatch rate (below 5%), and its contact type is an n-type Schottky contact. When a positive electric field is applied, the Schottky contact type undergoes a transition from n-type to p-type. Conversely, when a negative electric field is applied, the Schottky barrier experiences a significant reduction and transforms from an n-type Schottky barrier contact to an Ohmic contact. The research results in this article will offer valuable theoretical insights for the design and fabrication of electronic optical devices, including field-effect transistors and photodetectors.