The electronic properties and interface contact of graphene/WSSe van der Waals heterojunction by means of tuning the interlayer distance and external electric field were studied by the firstprinciples calculation method. The electronic properties of constituent monolayers can be retained in graphene/WSSe heterojunction because of the van der Waals force. A small band gap value (7 meV) can be found in the Dirac cone of graphene in graphene/WSSe heterojunction. The builtin electric field generated by the charge transfer plays a key role in the effective hindrance of photoexcited carrier recombination. The graphene/WSSe heterojunction possesses enhanced optical absorption in the visible light range compared with two freestanding monolayers, implying its potential application in optoelectronic device. Besides, the graphene/WSSe heterojunction displays the ntype Schottky contact characteristics at the equilibrium interlayer distance. Both the interlayer distance and external electric field can be used to modify the Schottky barrier height and contact types of graphene/WSSe heterojunction, and effectively adjust the Dirac cone position of graphene. The research in this paper provides a theoretical basis for the fascinating applications of graphene/WSSe heterojunction in the fields of nanoelectronic and optoelectronic devices.