Supercapacitors (SCs) are highly efficient energy-storage devices that enable rapid energy storage and release through ion adsorption at the electrode-electrolyte interface or fast faradaic reactions. Despite their great application potential, the development of this novel electrochemical energy storage technology has been limited by insufficient understanding of the fundamental charge storage mechanisms. Synchrotron radiation has a number of excellent characteristics, such as high brightness and coherence, wide energy range, and large redundant space for equipment integration; thus, various material characterization techniques based on synchrotron radiation have been developed. These techniques can provide the morphological structures, particle sizes, crystal structures, electronic structures, and local coordination environments of specific material elements as well as powerful technological support for in situ/in-operando material studies. This review introduces the application of in situ synchrotron radiation characterization methods applied to SC research in recent years. These methods include in situ X-ray diffraction (XRD), in situ X-ray absorption spectroscopy (XAS) and in situ small-angle X-ray scattering (SAXS). This article also presents an outlook for future applications of in situ X-ray imaging and pair distribution function techniques and discusses the prospects and key roles of in situ synchrotron radiation techniques in designing high power/energy density electrode materials for advanced SC devices.