The invention discloses a liquid level retaining device in an electroplating tank. The liquid level retaining device comprises a water fender, a mounting base and an elastic sealing body. The width of the water fender is greater than that of a through opening of an upper tank. The mounting base is arranged in the upper tank and is suitable for detachably mounting a wall face, in parallel with the upper tank and with the through opening, of the water fender into the upper tank. The elastic sealing body is fixed to the surface of the side, facing the through opening, of the water fender and arranged in a manner that the elastic sealing body corresponds to the two sides and the lower side of the through opening. The surface of the side, facing the water fender, of the elastic sealing body and the water fender form a sealing inner cavity. The surface of the side, backing against the water fender, of the elastic sealing body serves as a sealing face. Filler is packed into the sealing inner cavity so that the sealing body can be strutted. The sealing face can be attached to the wall face with the through opening in a sealing manner, so that a solution in the upper tank is disconnected from a solution in a backflow tank. Due to the fact that the filler is packed into the sealing inner cavity and the sealing body is kept in the strutted state for a long time, no fold phenomenon can occur; and consequently, the outer surface of the sealing inner cavity and the side wall of the upper tank can be in the sealed state, and the liquid level of the electroplating solution in the upper tank is kept not declining.