Abstract: Electrochemical interfaces are the core of various important fields, such as energy conversion and storage, biochemistry, sensors, and corrosion. The investigations of the structure-performance relationship of electrochemical solid-liquid interfaces have become a hot topic yet extremely challenging due to the fact that the interfaces are ultrathin, highly dynamic and extremely complex. Mass spectrometric techniques coupled with electrochemistry are powerful and have been widely applied in investigations of mechanisms of electrochemical reactions. However, traditional mass spectrometry (MS) is difficult to characterize the electrode-electrolyte interfaces in an in situ manner due to inherent limitations existing in their ionization processes. In recent years, the state-of-the-art in situ liquid time-of-flight secondary ion MS (ToF-SIMS) based on high-vacuum compatible microfluidic devices has been developed to tackle with this challenge. This review mainly reviewed the principle, characteristics and rapid development of in situ liquid ToF-SIMS in real-time and in situ investigations of electrochemical solid-liquid interfaces during the past decade. In situ liquid ToF-SIMS possesses shallow information depth (nm), high temporal resolution (μs) and high detection sensitivity (10^-6-10^-9). Besides, it ionizes the electrochemical interfaces in a truly in situ manner and provides direct molecular evidences of chemical evolution of both electrode/electrocatalyst surfaces and reactants/intermediates/products in electrolytes at the interfaces simultaneously. Being attributed to its uniqueness, in situ liquid ToF-SIMS has become a powerful and versatile molecular "eye" in in situ and real-time tracking dynamic electrochemical solid-liquid interfaces, such as capturing electrochemical reaction intermediates, identification of electrocatalytic active sites, probing fine structures of electrochemical double layers, and unraveling the formation chemistry of solid-electrolyte interphases in batteries. Further innovations of microfluidic electrochemical devices and ToF-SIMS instruments are desired to promote the enhanced performance and wider applications of in situ liquid ToF-SIMS in the electrochemical field, and in situ liquid ToF-SIMS will make significant contributions to the understanding of the structure-performance relationship of interfaces in complex electrochemical assays and guide the engineering of better electrochemical interfaces in important fields, such as electrocatalysis and batteries.