The effect of stress concentration was analyzed by finite element method for configuration of reinforcement, backing strip, tack welding and root opening of welded joint with backing strip in liner plate of power plant, offshore structure and steel bridge. The major findings are summarized as follows. The stress concentration factor(SCF) is the largest in root portion of welded joint with backing strip. The stress concentration factor(SCF) is decreased when the height and the width of reinforcement is decreased or the toe angle is increased in welded joint with backing strip. The stress is disturbed by the backing strip and tack welding in the welded joint. The stress concentration factor is increased as the root opening and the misalignment become larger in the welded joint with backing strip respectively.