Thermal protection materials, with their excellent thermal insulation and mechanical properties, have been widely used in the aerospace field. However, during the service life of reusable vehicles, impacts from airborne ice, raindrops, or even debris falling from the vehicle itself can cause damage to the surface and interior of the thermal protection materials, severely compromising the safety of the vehicle. Therefore, there is an urgent need for a non-destructive testing and evaluation technique to ensure the quality of thermal protection materials. Considering the challenges posed by the porous structure and thermal insulation properties of thermal protection materials, which result in rapid localized heating under non-uniform heating and significant lateral heat diffusion effects, this paper proposes an infrared pulse thermography method based on optical flow imaging. This approach aims to mitigate the interference caused by lateral heat diffusion and enhance the accuracy and reliability of defect detection in thermal protection materials.Transverse heat flow suppression (THFS) technique based on the optical flow method is proposed and applied to infrared pulse thermography, resulting in infrared pulse thermography optical flow imaging (Fig.1). This approach aims to mitigate the effects of transverse heat flow and enhance the detection accuracy of thermal protection materials. First, heat flow vector equations along the X and Y directions on the surface of thermal protection materials are derived using the optical flow method, and the inverse heat diffusion equation is formulated. Next, amplitude and phase feature images in the frequency domain corresponding to the surface of the thermal protection materials are obtained using the FFT and THFS coupling algorithm (Fig.2). Finally, the defect location and size are quantified using a local threshold segmentation method.Based on the above method, a three-dimensional simulation model was constructed using COMSOL Multiphysics software (Fig.3(a)), and non-uniform pulse excitation was applied. Through comparative studies of the simulation results, the differences in normalized FFT amplitude/phase and normalized FFT-THFS amplitude/phase (Fig.5) were analyzed. It was found that the proposed method effectively reduces the impact of uneven heating and lateral thermal diffusion, enhancing the normalized contrast between defective and non-defective regions. An infrared pulse thermography testing platform (Fig.8) was set up for experiments. Detailed comparisons were conducted on the relationships between the signal-to-noise ratio (SNR) of different feature parameters and defect diameter and depth (Fig.13), the relationships between the SNR of different feature parameters and the diameter-to-depth ratio of defects (Fig.14, Fig.15), and the effects of defect local threshold segmentation (Fig.16). The proposed method improves the SNR and accuracy of defect detection, enabling the quantified defect size to be closer to the actual size.This paper proposes an infrared pulse thermography optical flow imaging method with lateral heat flow suppression based on the optical flow method. First, the fundamental principles of Thermal Heat Flow Suppression (THFS) are elaborated using the optical flow method, along with the introduction of a 3D thermal wave model under non-uniform linear pulse heat flow excitation. To effectively extract defect features, the thermal wave image sequence is processed using Fast Fourier Transform (FFT), and the normalized FFT amplitude/phase is compared with the normalized FFT-THFS amplitude/phase. Simulation results demonstrate that THFS significantly reduces the impact of lateral heat diffusion, enhancing the contrast between defect and non-defect regions. Finally, infrared pulse thermography optical flow imaging was applied for non-destructive testing and evaluation of thermal protection material specimens with artificial flat-bottom holes. Experimental results show that the proposed method can effectively detect defects with a minimum diameter-to-depth ratio of 5 and a minimum diameter of 6 mm. The maximum detection error for defect diameter was reduced from 12.67% to 5.12%, and the defect detection signal-to-noise ratio was improved by up to 17.98%. These results confirm that infrared pulse thermography optical flow imaging effectively mitigates the interference of lateral heat diffusion and improves the accuracy and effectiveness of defect detection in thermal protection materials.