Graphene-based　van　der　Waals　(vdW)　heterostructures　have　shown　great　potential　in　electronic　and　optoelectronic　nanodevices.　Herein,　we　investigate　the　electronic　property　and　Schottky　barrier　of　graphene/GeN3　vdW　heterostructure　by　first-principles　calculations.　It　is　noted　that　the　electronic　natures　of　graphene　and　GeN3　monolayers　are　well　preserved　in　the　heterostructure　lattice　due　to　the　weak　vdW　interaction.　Interestingly,　the　p-type　Schottky　contact　in　graphene/GeN3　heterostructure　with　a　barrier　height　of　0.21　eV　can　be　effectively　tuned　by　both　vertical　and　horizontal　strains.　Herein,　the　carrier　concentration　in　the　graphene　layer　reaches　similar　to　10(13)　cm(-2)　level　by　strain　engineering.　It　is　noteworthy　that　the　designed　optoelectronic　field-effect　transistor　based　on　graphene/GeN3　heterostructure　exhibits　distinguished　responsivity　of　0.297　AW(-1)　and　impressive　external　quantum　efficiency　of　54.5%　under　illumination　based　on　further　non-equilibrium　Green＇s　function　simulations.　Our　findings　are　of　utmost　significance　for　the　metal-semiconductor　vdW　contact　and　corresponding　applications　in　high-performance　electronic　and　optoelectronic　devices.