Abstract: For the demand of quantitative detection of welding crack defects in crane metal structures, the application of infrared thermography test in the quantitative identification of defect depth was studied. The technical principles of pulsed thermography and pulsed phase thermography were described successively. The thermal analysis model of the specimen containing crack defects was established and simulated based on COMSOL software, then the temperature responses of the defect areas at different depths were obtained.On this basis, the prediction accuracy of the defect depth by pulse thermography and pulse phase thermography was compared and analyzed.The results show that the pulse thermography has a good effect for shallow defects by using the time corresponding to peak temperature difference to predict the defect depth, and the quantitative identification of defects with large depth can be realized by using the pulse phase thermography based on the relationship between the blind frequency and the defect depth to predict the defect depth.