The invention discloses a steel plate connecting device comprising a connection assisting plate used for connecting at least two steel plates which are to be connected together. The connection assisting plate is provided with at least one contact face used for being attached to the to-be-connected steel plates. Connecting devices are arranged between the to-be-connected steel plates and the connection assisting plate for fixing the steel plates attached to the contact faces. The at least two to-be-connected steel plates are connected with the same connection assisting plate so that the heightdifference between the steel plates which are to be connected together can be controlled through the contact faces arranged on the connection assisting plate; meanwhile, by arranging the connecting devices, the horizontal position relation between the to-be-connected steel plates can be controlled; after the positions of the to-be-connected steel plates are determined, the to-be-connected steel plates are fixed through the connecting devices, and welding operation is conducted after fixing; and local cracks of a welding structure can be avoided, the weld penetration faces is stable relatively,and tensile bearing capacity is improved.