The invention discloses an automatic balancing device for a wharf boat. The automatic device enables the wharf boat to keep balance automatically when a movable front steel support shifts greatly. The automatic balancing device comprises a movable steel approach bridge (1) disposed on the wharf boat (5). The front end of the movable steel approach bridge (1) is provided with a movable steel approach bridge front support seat (4) connected with the wharf boat (5). An automatic balancing rail (3) protruding upwardly is arranged on the wharf boat (5). An automatic balancing support (2) connected with the automatic balancing rail (3) is disposed at the lower end of the movable steel approach bridge (1). The activity ranges, on the wharf boat (5), of the automatic balancing support (2) and the movable steel approach bridge front support seat (4) are located on two sides of a gravity center line (5.1) of the wharf boat.