The inner wall corrosion of pipeline causes great serious problems to the safety production of chemical enterprises,so it is very important to estimate the inner wall corrosion defect depth.Eddy current thermal imaging technology is used to detect and evaluate the corrosion defects in different depths of the inner wall.COMSOL was used to establish 3D finite element models of defects with different depths,and temperature signals of defects with different depths were extracted during the cooling stage.Through data normalization method,the influence of defect depth on heat conduction was analyzed.At the same time,the numerical simulation results were verified by eddy current thermal imaging experiment,and the depth of corrosion defects was estimated by using the integral value of transient temperature attenuation signal as the characteristic quantity.The results show that the deeper the defect depth,the faster the temperature attenuation rate in cooling stage and the smaller the integral value of temperature attenuation signal in transient state.At the same time,for the 4 mm pipe with a wall thickness,the corrosion defect with a diameter of 6 mm and a minimum depth of 1.5 mm can be identified from the original thermal image.