The invention relates to a large-power modularized DC power supply device and a control method thereof. The large-power modularized DC power supply device is composed of three two-way power units and a transformer with zigzag connection. Each two-way power unit includes twelve reverse-conducting IGBTs forming six bridge arms, wherein each bridge arm is connected with primary windings Tx1, Tx2 andTx3 of the transformer with zigzag connection. A voltage and current sensor is also connected. The AC-side voltage of the two-way power unit is superposed with the phases of fifteen secondary windings in zigzag connection; a filter capacitor is connected between every two phases to generate three-phase symmetrical 18 ladder wave AC line voltages; and the DC sides of the two-way power units are connected with each other in parallel. The power supply device and the control method thereof have the advantages of stable DC output voltage, fast system response, good controllability, and less harmonic wave pollution at the AC sides, and particularly can achieve energy feedback from the DC side to the AC side and two-way energy transmission between the DC side and the AC side, thereby achieving positive effect on energy saving and emission reduction.