The invention provides a track type circular bare wire suspending type power supplying method of a portal crane of a bridge precast beam field. The method specifically comprises the steps of fixing one end of a line sliding device bracket to the portal crane, and connecting the other end of the line sliding device bracket to the portal crane through an adjustable rope fastener; mounting the line sliding device to the line sliding device bracket; adjusting the contact closeness of the line sliding device and a sliding line through the adjustable rope fastener; connecting the line sliding deviceand a cable of the portal crane; arranging a door frame at each of two ends of the portal crane; arranging an electric wire pole between the two door frames; arranging a sliding line support on the electric wire pole; and aerially arranging, supporting and fixing the sliding line and a power transmission cable through the electric wire pole and the door frames. The method aims at solving the problems that most of the sliding contact type sliding lines are copper bare wires which are high in cost, and a sliding contact device is complex to manufacture and inconvenient to maintain.