In this paper, carbon fiber reinforced polymer (CFRP) is tested using lock-in thermography, which is excited by an induction coil. A impact-damaged CFRP plate was available and measured as a function of the angle between a linear excitation coil and the main fiber directions. The amplitude and phase images of high signal-to-noise ratio (SNR) was obtained by Fast Fourier Transform (FFT). The relationship between angle sensitivity of included angle and crack shape is analyzed. The results show that the circular symmetry is basically maintained when the defect is linear. When the structure of defects is similar to that of bifurcated trees, the angular distribution is quite different, which are consistent with the results of X-ray imaging.