The electronic properties of MoSe2/MnPSe3 van der Waals heterojunction are investigated under vertical electric field. By first principles calculation we find MoSe2/MnPSe3 van der Waals heterojunction is a type-II semiconductor. The band gap and band offset of this heterojunction can be controlled in a large energy range by applying vertical electric field. The direct band gap from 1.48 eV to 0.00 eV and type-II characters can be maintained under the electric field from −0.1 V/Å to 0.5 V/Å. The semiconductor-semimetal phase transition is observed under the vertical electric field. Therefore, we deduce that MoSe2/MnPSe3 van der Waals heterojunction can be used in the fields of solar cells and photodetectors.