The horizontal displacement more than 16cm occurred on the facing of a 20m high reinforced soil retaining wall that was under construction for the purpose of the alignment improvement of the existing national highway located in Hyogo, Japan. In this paper, the causes of the excessive deformation, together with the numerical examination into countermeasures are in detail described. First, various site investigations and laboratory tests were carried out to manifest the current state of the reinforced soil retaining wall. Second, the deformation behavior of the wall was simulated by performing numerical analysis. Finally, an appropriate countermeasure to prevent further development of the wall deformation was proposed by predicting the stress-strain behavior of the reinforced soil retaining wall with the remedial work.