Abstract: In order to research the influence of SiO2 on thermal stress of multilayer GaN epitaxial wafer, the surface stresses in sapphire/AlN/GaN and sapphire/SiO2/AlN/GaN epilayers with a diameter of 40 mm were respectively calculated and simulated by the finite element modeling method. The epilayer stress distribution in the radial and axial directions of two epilayers were analyzed with the same other structure parameters, and the thermal stress influence factor was analyzed. The results indicate that the epitaxial wafer thermal stress was uniformly distributed in the radial direction and there were mutations on the substrate and epitaxial layer in the axial direction at 1 200 ℃. Finally the influence of the growth temperature,the GaN and AlN transition layers thickness and the sapphire substrate thickness on surface thermal stress was analyzed.