The finite element method is introduced to study the three-dimensional temperature fields for bilayer structure of diamond/ZnSe substrate films irradiated by laser-induced transient surface grating. The temperature fields are compared for different thickness of diamond film. It is shown that the thickness of the diamond films has great influence on the temperature distribution of the films. With the thickness increase of the diamond film,the peak of temperature field in the sample increases and the twice heating becomes more obvious.