The invention, which belongs to the technical field of power supply of the electrical railway traffic, provides a protective relaying device and method of a direct-current traction substation. With the device and method, a problem of short service life of a direct-current switch can be effectively solved. The device is capable of identifying and distinguishing a permanent fault and an instantaneous fault. The device relates to an alternating-current switch QFJ of a three-phase inlet wire K of an existing direct-current traction substation, a voltage transformer YH of a direct-current bus B, a direct-current switch QFZ1 of a direct-current feeder line I K1 and a current transformer I LH1, and a direct current switch II QFZ2 of a direct-current feeder line II K2 and a current transformer II LH2. An input terminal of a protective relaying device RP is connected with a measuring terminal of the voltage transformer YH and measuring terminals of the current transformer I LH1 and the current transformer II LH2; and an output terminal of the protective relaying device RP is connected with a control terminal of an alternating-current switch QFJ and control terminals of the direct-current switch QFZ1 and the direct current switch II QFZ2. The device and method are mainly applied to protective relaying of the direct-current traction substation.