A DC-DC power conversion apparatus and a DC-DC power conversion method are provided. The DC-DC power conversion apparatus includes a switching circuit, a main transformer circuit, a main rectifier circuit, an auxiliary transformer circuit and an auxiliary rectifier circuit. The switching circuit provides an input power to a primary winding of the main transformer circuit or a primary winding of the auxiliary transformer circuit by time-division. An AC input terminal of the main rectifier circuit is coupled to a secondary winding of the main transformer circuit. An AC input terminal of the auxiliary rectifier circuit is coupled to a secondary winding of the auxiliary transformer circuit. A power output terminal of the auxiliary rectifier circuit is coupled to a reference voltage terminal of the main rectifier circuit for lifting a voltage of the power output terminal of the main rectifier circuit.