The invention discloses a bridge lighting device capable of achieving automatic adjustment. The bridge lighting device comprises an installing rack and a lamp bracket matched with the installing rack; a shifting groove is formed in the installing rack, penetrating holes communicating with the shifting groove are formed in the right end face of the installing rack, inserting rods matched with the penetrating holes are arranged on the left side of the lamp bracket, the right end walls of the upper portion and the lower portion of each inserting rod are provided with first magnets, and second magnets capable of achieving mutual attraction with the first magnets are arranged on the left side of the lamp bracket; a sliding frame is installed in the shifting groove in a left-right sliding mode, and a left-right cut-through communicating groove is formed in the midpoint of the sliding frame; a position guiding rod is fixedly installed on the portion, located at the vertical midpoint, of the shifting groove and divided into a left position guiding portion and a right reducing portion, and the position guiding portion penetrates into the communicating groove.