Abstract: Aiming at locating those typical defects possibly existing in large scale wind turbine blade materials, this article established an axial symmetrical non-steady state heat conduction model, which described how to test air holes inside the wind turbine blades using pulse infrared imaging, and got the temperature field and heatflux field of any time during pulse heating-cooling stage, as well as the surface temperature and temperature differences between defective area and sound area by ANSYS simulation calculation. From theoretical calculation, the author also reveal the mechanism of inner defects test by infrared imaging, which also validate the feasibility of NDT of inner defects by using infrared imaging.