The invention discloses a differential projection current passage switching method for a main transformer of a pumped storage power station. The protection range applicable to the pumped storage powerstation comprises main transformer differential protection of a commutation knife, a dragging knife, a dragged knife, a power generator outlet switch and an electrical brake switch. The current passage switching method comprises the steps of a) arranging a high-reliability current passage switching logic in a main transformer differential projection device; b) arranging a logic in a machine set sequence control system, and matching with main transformer differential protection to achieve the purpose that the fault sequence also can be reduced even a fault occurs in the current passage switching logic; and c) determining a position connection point taking method employed by the current passage switching logic, and fully employing a site condition to improve switching reliability. The differential projection current passage switching method has the advantage of high reliability and is applicable to a running condition that the main transformer differential projection current passage ofthe pumped storage power station is frequently switched, and the problem that the mis-switching of the current passage in the prior art to cause tripping of the main transformer is solved.