The numerical simulation of non-destructive testing of the materials has made considerable progress in the recent years. This simulation allows not only to increase the efficiency and the potential of the non-destructive testing methods, but also to expect the results of a particular technology and to define the most efficient conditions of achievement, while reducing the costs of progress. The purpose of this presentation is to show the important contribution of the computer simulation as regards the auscultation of the reinforced concrete slabs by GPR technique. The cases of the water infiltration and the chloride ions as well as the delaminations are considered.