A lightning protection device for a direct-driven wind turbine generator system, comprising: a lightning arrester arrangeable on a nonmetallic blade and configured to receive a lightning current, and a blade down lead electrically connected to the lightning arrester, wherein the lighting protection device further comprises: a first lightning current conducting component, electrically connected to the blade down lead and connectable to an outer surface of a generator rotor in an insulation manner; wherein the first lightning current conducting component comprises a first conducting end and a second conducting end; a second lightning current conducting component, connectable to the outer surface of the generator rotor and an insulated nacelle cover having a surface insulated from the second lightning current conducting component in insulation manner, and electrically connected to the first lightning current conducting component via a metal conductor; and a lightning protection down lead, configured to electrically connect the second lightning current conducting component to a grounding component arrangeable inside a tower, to discharge the lightning current to ground by the grounding component, wherein the first conducting end is one of a metal arc-shaped electric brush track with a preset radian and a first lightning protection electric brush, and the second conducting end is the other one of the metal arc-shaped electric brush track with the preset radian and the first lightning protection electric brush; wherein the lightning protection device further comprises a first insulating component arrangeable on the outer surface of the generator rotor and close to the blade; and the first conducting end is arrangeable at a root of the blade and is electrically connected to the blade down lead, the second conducting end is arranged on the first insulating component and electrically connected to the metal conductor, and the first conducting end is in a sliding contact with the second conducting end during the rotation of the blade; and wherein the lightning protection device further comprises a second insulating component arrangeable on the outer surface of the generator rotor and close to the insulated nacelle cover; and the second lightning current conducting component comprises a third conducting end and a fourth conducting end, the third conducting end is arranged on the second insulating component and is electrically connected to the metal conductor, the fourth conducting end is arrangeable on the insulated nacelle cover and is electrically connected to the lightning protection down lead, and the third conducting end is in a sliding contact with the fourth conducting end during the rotation of the generator rotor. a first lightning current conducting component, electrically connected to the blade down lead and connectable to an outer surface of a generator rotor in an insulation manner; wherein the first lightning current conducting component comprises a first conducting end and a second conducting end; a second lightning current conducting component, connectable to the outer surface of the generator rotor and an insulated nacelle cover having a surface insulated from the second lightning current conducting component in insulation manner, and electrically connected to the first lightning current conducting component via a metal conductor; and a lightning protection down lead, configured to electrically connect the second lightning current conducting component to a grounding component arrangeable inside a tower, to discharge the lightning current to ground by the grounding component, wherein the first conducting end is one of a metal arc-shaped electric brush track with a preset radian and a first lightning protection electric brush, and the second conducting end is the other one of the metal arc-shaped electric brush track with the preset radian and the first lightning protection electric brush; wherein the lightning protection device further comprises a first insulating component arrangeable on the outer surface of the generator rotor and close to the blade; and the first conducting end is arrangeable at a root of the blade and is electrically connected to the blade down lead, the second conducting end is arranged on the first insulating component and electrically connected to the metal conductor, and the first conducting end is in a sliding contact with the second conducting end during the rotation of the blade; and wherein the lightning protection device further comprises a second insulating component arrangeable on the outer surface of the generator rotor and close to the insulated nacelle cover; and the second lightning current conducting component comprises a third conducting end and a fourth conducting end, the third conducting end is arranged on the second insulating component and is electrically connected to the metal conductor, the fourth conducting end is arrangeable on the insulated nacelle cover and is electrically connected to the lightning protection down lead, and the third conducting end is in a sliding contact with the fourth conducting end during the rotation of the generator rotor.