The invention belongs to the protection field of DC bias technologies of transformers, and specifically relates to a DC bias suppression device with dual protection and a DC bias suppression method. The device comprises a transformer neutral line grounded switch K1, a DC blocking switch K2, a DC blocking capacitor C, a protection gap loop, a transistor protection loop, a zinc oxide arrester R, a bypass protection switch K3, a first current transformer CT1, a second current transformer CT2, a signal conditioning unit, a control unit, and a drive unit. The method comprises the steps of (1) detecting a DC component; (2) comparing the detected DC component with a threshold, and performing a corresponding action; (3) detecting an AC; (4) comparing the detected AC with a threshold, and performing a corresponding action; (4) determining whether each action can be performed normally, and performing a corresponding action; and (5) after an AC power grid fault is handled, resetting the system, and returning to step (1).