Finite element analysis software ANSYS is used to calculate the stresses in GaN film on sapphire，and the results was proved to be reasonable by theoretical calculation. The stress distribution of GaN film on sapphire is simulated. The dependence of stress on deposition temperature, film thickness and substrate thickness is analyzed. The effect of non-uniform temperature distribution on stresses is also discussed. The results show that a largest thermal stresses appears in the center, a sharp reducing of stress occurs at the film edge and the rest parts are relatively uniform. When the deposition temperature increases, the film thickness reduce or the substrate thickness increases ,thermal stresses will increase. When the radial direction temperature has a non-uniform distribution in the sapphire substrate, the film stress will increase, and the larger difference of temperature is, the larger thermal stress in the film will be.