The present invention discloses a direct-current power transmission protection device, including a resistor unit and a bidirectional circulation current switch unit, and the resistor unit and the bidirectional circulation current switch unit being connected in parallel to form the protection device, where at least one resistor is cascaded to form the resistor unit, and at least one bidirectional circulation current switch is cascaded to form the bidirectional circulation current switch unit. In addition, the present invention also provides a converter including the protection device, and at least one protection device is connected in series in each phase unit. The present invention provides the protection device, the converter and a protection method for flexible direct-current power transmission, which can rapidly and effectively suppress direct-current short circuit current and damp current oscillation, and not only can better protect equipment safety, but also can greatly shorten fault current attenuation time, thus shortening direct-current shutdown time and further decreasing economic loss and system destabilization risk caused by shutdown to the max. Moreover, the protection device is structurally simple and low in cost, and has good implementability and economic efficiency.