Catalysis of water, normally occurring at the interface, is crucial for the development of renewable energy and the environmental protection. Understanding the structures and chemical/physical properties of interfacial water during catalysis is of paramount importance for the sustainable development of human society, such as clean energy, wastewater treatment, and etc. However, owing to its complexity structure and mysterious property, the effect of water during catalysis is still an open question. The role of water during reactions, as reactant, catalyst, solvent, or both, has not been resolved. Recently, with the fast-development of in-situ experimental techniques and the computational capacity, the scientists started to investigate the behaviors of interfacial water using the real-time characterization and theoretical modeling at the atomic level, which provides the evidences and pictures to understand the effects of interfacial water. This paper will briefly introduce the current opportunities and challenges in studying the interfacial water, and the latest development and facing difficulty in experiment and theory, which will be beneficial for the future design of efficient catalysts for their applications in water.