The thermal stress analysis around cavities which are formed near the interface in perpendicular direction by the various effects on one of the plate of two material-composite plates used mostly in many applications was attained. Particularly, the composite plates consisting of steel and stainless steel plates which are used in the body of reactors in nuclear power plants were modelled in this study. The analyses were performed by Finite Element Method. The finite element model was validated using the analytical solution derived from the solution in the literature and mesh refinement. As a result of this, according to the geometry and position of the cavities, the variations of thermal stress intensity factor were obtained. Here, the selected type of cavity has been identified in the literature and it was detected on the real structure.