Abstract: The stress concentration, density non-uniformity and internal concentrated defects of GIS/GIL insulators may be the main reasons threatening the safe operation of GIS/GIL. It is urgent to study the detecting methods. The cause and detecting methods of stress concentration, density non-uniformity and internal concentrated defects of GIS/GIL insulators are analyzed in this paper. The research progress of ultrasonic detecting method for epoxy composite materials commonly used in GIS/GIL insulators is systematically summarized, including ultrasonic propagation characteristics such as longitudinal wave velocity, detection depth, sensitivity, first critical angle and longitudinal critical refracted wave penetration depth. The ultrasonic detecting method of stress is introduced including acoustoelastic effect and coefficient of ultrasonic longitudinal critical refracted wave, detecting method of subsurface stress for GIS/GIL insulators by acoustic-distance difference method using longitudinal critical refracted wave and thermal stress nephogram, and detection of parallel stress by longitudinal wave reflection method and vertical stress by longitudinal wave penetration method for three-post insulators. The ultrasonic detecting method of internal concentrated defects is introduced including imaging of internal defects for GIS/GIL insulators by longitudinal wave reflection method, surface defects detection by ultrasonic longitudinal critical refracted wave method and interfacial defects detection by longitudinal wave oblique incidence method. The ultrasonic detecting method of density uniformity is introduced such as density nephogram of basin insulators by longitudinal wave reflection method. The key technologies and basic theories which are widely used in GIS/GIL insulators in the future and need to be solved urgently for ultrasonic detection are as follows: to research and develop ultrasonic probe that is fewer-crest, high-frequency and high-energy, technology of full range ultrasonic fast imaging of insulators, ultrasonic detection of multi structure and multi position, residual stress measurement with stress relief method, and the coupling theory of density and residual stress.