Abstract: Infrared technology for nondestructive testing under linear frequency modulated excitation is a new detect technology. The shortcomings of the traditional infrared NDT methods can be avoided and different detects can be defected by this method. In order to research the application of infrared technology for nondestructive testing under linear frequency modulated excitation, a two-dimensional heat conduction model was established by finite volume method. The temperature field of the model was obtained under linear frequency modulated excitation. The FFT algorithm was applied to the surface temperature of the model and then the phase was obtained. The influences of Chirp modulation time, heating intensity, material depth, height and width on the phase difference were respectively revealed. It is important for the application of infrared technology for nondestructive testing under linear frequency modulated excitation.