Critical zone science has become one of the important research areas in surface-Earth system science. Karst critical zone (KCZ) is a typical case, representing a unique type of the Earth’s critical zone, covering about 15.2% of the global ice-free continental land. However, there is still a lack of related discussions on the structure and characteristics of the KCZ. This paper sorts out the background and development processes of the concept and summarizes its characteristics. The KCZ is a type of Earth critical zone shaped by the material circulation and energy flow at the interface of lithosphere, hydrosphere, atmosphere, biosphere, and pedosphere in soluble rock areas (carbonate rock, sulfate rock, halite, etc.). The range of KCZ extends from the vegetation canopy to the bottom of the karst aquifer in soluble rock areas. From the perspective of karstology, it includes vegetation, soil, epikarst, vadose, and saturated zone, which is sensitive to environmental changes and has surface and subsurface double geological structure, special geochemical processes characterized by coupling cycle of carbon, water, and calcium. By comparison, the KCZ have eight important features, which distinguish it from non-KCZ. They are also important issues to be concerned with in relevant monitoring, simulation, mapping, as well as the structure composition and evolution, and function and service research of the KCZ.