To solve the issue of complex image reconstruction at a small sampling rate due to the high repetition rate and redundancy of cylinder head inner wall thermal field data, a thermal fatigue damage detection method for cylinder head inner wall with a small sample is proposed via fusion of multiple single-scale reconstructed images. The proposed method begins by correlating the thermal scatter pattern of the inner wall with the total radiant energy of its outer wall at various scales to obtain multiple reconstructed images of the cylinder head inner wall. Then, the image fusion technology is used to fuse the reconstructed images of the inner wall at different scales to obtain the fused images of the cylinder head inner wall. The paper demonstrates the advantageous performance of the proposed method in small sampling rate image reconstruction by comparing the results of inner wall image reconstruction at various sampling rates. The effects of different fusion weight coefficients on the fused images are also discussed. The outcomes of the experiments demonstrate that the proposed method may detect the thermal fatigue damage zone of the inner wall at a lower sampling rate. The peak signal-to-noise ratio and contrast ratio of the proposed method are enhanced by 9.62% and 26.13%, respectively, compared with those of the traditional correlation method when the number of samplings is 500. The proposed method also has the distinct benefit of postponing the deterioration of the reconstructed picture quality, thereby resolving the problem of thermal fatigue damage detection caused by insufficient data gathering in real-world applications.