Abstract: Considering the energy and environmental issues faced by human society, hydrogen has become increasingly important, and electrocatalytic water splitting is considered to be an ideal way to solve these energy issues. However, although most electrocatalysts will undergo a structural evolution when in service conditions, our understanding of the service behavior of catalysts is limited. To design highly active catalysts, operando characterization techniques must be used to study their dynamic structural evolution. Today, the development of synchrotron radiation devices has reached an important stage. Synchrotron-radiation-based X-ray characterization, which has high energy, large flux, and excellent collimation compared with the ordinary laboratory X-ray source, can capture the precise structure of catalytic materials. In this review, we present the development status of synchrotron radiation devices and the basic principles of operando X-ray absorption spectroscopy, X-ray diffraction spectroscopy, and X-ray photoelectron spectroscopy based on synchrotron radiation. In addition, we highlight studies related to the dynamic service behavior of water-splitting catalysts under real conditions and list a variety of operando studies of typical water-splitting catalysts, including NiFe hydroxide/(oxy)hydroxides, perovskite oxides, spinel oxides, and noble-metal-based catalysts. The use of operando X-ray techniques deepens our understanding of the catalyst reaction mechanism and provides a basis for identifying the dynamic structure–performance correlation of catalysts. We summarize the problems and challenges of operando X-ray-based techniques in complex electrochemical environments and propose the prospect of an advanced synchrotron radiation facility for operando X-ray characterization. With the development of the next-generation synchrotron radiation facility, adequately using this advanced X-ray light source to study the dynamic structure–activity correlation of catalytic materials throughout their life cycle to achieve the precise design and synthesis of complex pre-catalysts will advance the development of this field by enabling greater refinement and control.