We present simulations of quantum transport in graphene p-n junctions (pnJs) in which moire superlattice potentials are incorporated to demonstrate the interplay between pnJs and moire superlattice potentials. It is shown that the longitudinal and Hall resistivity maps can be strongly modulated by the pnJ profile, junction height, and moire potentials. Device resistance measurements are subsequently performed on graphene/hexagonalboron-nitride heterostructure samples with accurate alignment of crystallographic orientations to complement and support the simulation results.