Abstract: The hot air infrared NDT process is simulated by the ANSYS finite element method (FEM) for inner surface cracks in polyethylene pipes. The relationships between the surface temperature distribution with the defect size and with the defect location are determined. In order to validate the FEM simulated results for pipeline defects, an active infrared thermal imaging experiment platform based on hot air heating excitation was built. The results showed that the experimental results were in good agreement with the simulated ones. It demonstrated that FEM method could be used to investigate infrared thermal imaging technology, and it also could provide a computational model for inner defect infrared detection technique.