Abstract: Considering the reliability of diamond/ZnS infrared windows, it is very useful to know how much thermal stress and deflection exist in the structure. The stresses, curvature and deflection of thick diamond film bonded to zinc sulfide substrate at elevated temperature were predicted. An elastic strain numerical model was used in the calculation. The thermal stresses throughout the structure after bonding were shown for each condition. Also, the curvature and the edge to center deflection caused by thermal stresses were reported. Results show that when thickness ratio of diamond films to ZnS is about 17% and bonding temperature is higher than 250℃, the stresses within the ZnS substrate are predicted to exceed their rupture strength.