The invention discloses a main-transformer low-voltage-side busbar bridge grounding wire clamp, which comprises a busbar bridge clamp, a grounding hook, an insulating separator plate and an insulating window. The busbar bridge clamp has a double-layer structure, wherein one sides are connected together and the other sides are opened to form a clamp shape connected with a busbar bridge. The grounding hook comprises a vertical plate and an oblique plate. The vertical plate is fixed to the connection side of the busbar bridge clamp. The oblique plate is connected to the bottom end of the vertical plate and forms an oblique angle with the vertical plate. Three surfaces of the busbar bridge clamp at the opened side are provided with the insulating separator plate. The insulating separator plate and the vertical plate are connected by the insulating window. The main-transformer low-voltage-side busbar bridge grounding wire clamp of the invention has a simple structure, is low in cost and is easy to mount. Each of three phrases of the main-transformer low-voltage-side busbar bridge is equipped with one main-transformer low-voltage-side busbar bridge grounding wire clamp so as to make it convenient to hang a low-voltage-side grounding wire during maintenance of a main transformer, and usually because of the insulation closed design, it is guaranteed that there is no short-circuit fault risk, so the main-transformer low-voltage-side busbar bridge grounding wire clamp of the invention is of great significance to power grid maintenance safety and reliable power supply.