This paper presents a W mockup with an interlayer of diamond/Cu (DC) composite material. As a joining interlayer, DC composite material has high thermal conductivity and accommodative coefficient of thermal expansion. By adjusting the thickness of the DC layer and comparing different forms of armor, the optimal design is the brush armor mockup with a 1-mm-thickness DC layer. The thermal-structural behavior of this mockup was analyzed under the steady-state and transient heat flux by using ANSYS Workbench. The calculated temperature and stress indicate that the mockup can tolerate 10 MW/m2 steady-state heat flux at most. Then a transient heat flux (300 MW/m2 for 5 ms) is loaded on the top surface upon steady-state heat flux of 8 MW/m2. The surface temperature instantly rises to 2300°C, but a cracking trend is not shown at the loaded surface.